Re-add documentation of noise parameter formats.
Re-add 'mgv5_np_ground' noise parameters in group format.
Both these were deleted through auto-generation of conf.example.
Add note to builtin/mainmenu/dlg_settings_advanced.lua that this
documentation must be preserved.

Fix a typo pointed out by @thecow275.

Also, use the deprecated notification system which respects the
deprecated_lua_api_handling setting.

Disable the ability to connect to old servers by default to
improve password security.

If people still want to connect to old (0.4.12 and earlier)
servers, they can flip the send_pre_v25_init setting.

Add the ability to detect if we've tried to connect
to a server which only supports the pre v25 init protocol,
and show an apropriate error message. Most times the error
will already be catched at the serverlist level, the
detection mechanism only acts as last resort, because the
"Connection timed out" error message that would be shown
otherwise would be very confusing.

Automatic "fixing" of this condition is not desired,
as it would allow for downgrade attacks.

As already 161 of the 167 servers on the serverlist
support the new srp based auth protocol (> 96%),
the breakage should be minimal.

Follow up of commit

af301831 "Add option to not send pre v25 init packet"

Also change the pessimistic assumption of masterlist
server versions to optimistic, in order to avoid buggy
behaviour (favourites not in the serverlist would be
denied to connect to, etc).

* Multiline strings
* Table-concat instead of String-concats
* string.rep instead of loop-concat
* string.format %q instead of manual quotation by gsub
* Assert writeable files
* Generate new settings_translation_file

Avoids unreachable code linter warning by moving generation code
(of minetest.conf.example and settings_translation_file.cpp)
out of dlg_settings_advanced.

Due to passing the settings, also it avoids reading the settings file twice.

Instead of activating the code by changing the active if-clauses,
its activation is now done by uncommenting the loadfile() statement.

Recommend mod screenshot size in lua_api.txt
Adjust displayed screenshot size of texture packs
Document texture pack files in lua_api.txt

Fixes #4120.

The change keys dialog can't be left. It doesn't make
much sense to show it on Android in the first place,
therefore disable it, just like commit

aed70cb0 'Disable sound and key binding settings in "pause" menu on android'

has disabled it for the esc menu.

Fixes #4115.

Bug and whitespace error fixed (Zeno)

Also, fix a nil error that can happen sometimes in
menu_handle_key_up_down

@SmallJoker has noted a bug that servers from the (local) main menu
favorites list can't be opened.

This commit fixes the bug by disabling any main menu based protocol
checks for servers from the favorite list.

Also, it fixes a second bug that happens when a server from the
public serverlist doesn't send its supported protocol versions,
most likely because its running a minetest older than commit [1].
Then we have shown an error msg that the server has enforced
one specific protocol version. This was most likely not the case.

Of course, we can't do anything better than do an assumption on
the protocol versions if they are not known. That assumption
should however be closest to the most often occuring case as
possible.

Also, some little cleanups.

[1]: 5a0ed780 "Server: announce MIN/MAX protocol version supported to serverlist. Client: check serverlist"

Apply de morgan to simplify the logic.

 - Use local variables for tabs in place of globals
 - Merge together if statements where possible
 - Replace manual table searching code with indexof where possible

Additionally, fix misc. code style issues

The legacy init packet (pre v25) sends information about the client's
password that a server could use to log in to other servers if the
username and password are the same. All the other benefits of SRP of
protocol v25 are missed if the legacy init packet is still sent during
connection creation.

This patch adds an option to not send the v25 init packet. Not sending
the v25 packet means breaking compat with pre v25 servers, but as the
option is not enabled by default, no servers are affected unless the
user explicitly flips the switch. More than 90% of the servers on the
serverlist support post v25 protocols.

The patch also fixes a bug with greying out of non compliant servers
being done wrongly, the min and max params were mixed.

If the default value of a setting was empty,
it previously generated a trailing space.

The save button is now fully functional again when an error message
is shown.

After an invalid value is entered in the settings tab dialog, the GUI
label for the error message that is shown was partly overlapping the
'save' button, so that the top half of the button could not be clicked
on.

Changes:
- Accept setting an empty flags-type value in the settings tab
  if the variable specification permits it
- Don't accept substrings of flag values
  E.g. with values: 'one,two,three', 'hree', 'w', etc. used to
  be accepted. Not any more
- Don't accept flags with random pattern-matching special characters
  E.g. with values: 'one,two,three', 'on.', '(o)[n]e*' etc. used
  to be accepted. Not any more.

- Accept numbers prefixed with '+'
- Accept multiple spaces instead of just a single one where spaces are expected
- Allow flags to have an empty default value

Add the v3f type, currently is just a nice placeholder for string.
Currently undocumented, on wish of @PilzAdam, to support future changes.