Also remove some unused parameters/functions

Fixes #4397

Adds initial ingame gamepad support to minetest.

Full Formspec support is not implemented yet and
can be added by a later change.

Add documentation, move files to a proper place and avoid memory leaks.
Make it work with most kind of texts, and allow backgrounds too.

Doing it the other way round was a mistake, since it breaks
minetest.formspec_escape with escape sequences that contain
special characters.

This makes it work even if it contains escape sequences,
which didn't work before.

Also, change the escape character to the more standard \x1b
Thus, it can be used in the future for translation or colored text,
for example.

Thanks @ExcaliburZero for noticing. Fixes #3698.

Adds list-rings, a method to implement item sending between inventories via shift-click.
Nice insider feature: a ring consisting of a single inventory list serves as nice clean-up method.
Also adds them to minimal game, and the standard inventory.
Craft output slots are not supported.

Also, clean up surrounding code style
Replace by-value parameter passing with const refs when possible
Fix post-increment of iterators

* Move networkcode to a dedicated directory
* Rename clientserver.h to network/networkprotocol.h (Better name) and sanitize some includes
* Create object NetworkPacket
  * It stores command (opcode) and data separated
  * It also stores peer_id
  * Data reading can be done by using a streaming interface
* Change packet routing analysis
  * Remove old conditional analysis
  * Now uses function pointed analysis and add connection state ({Client,Server}::handlers)
  * Connection state permit to categorize condition to handle before analyze packets
  * Create a handler for depreciated messages, instead of duplicating code

Right mouse button behaviour for craft/inventory If right mousebutton clicked once then don't drop single items into slots. If right mouse button has been clicked and held a second time, drop items as the mouse is moved. In the second case (automatically drop/place items as mouse is moved) only auto-drop into blank slots, or slots that contain the same item.

The ratios between the sizes of form elements, including text, is now
fixed, aside from variations caused by rounding.  This makes form layout
almost fully predictable, and particularly independent of player's
screen size.  The proportions of non-text elements are the traditional
proportions.

For compatibility, the way in which element positions and sizes are
specified remains unchanged, in all its baroqueness, with one exception.
The exception is that the position of a label[] element is now defined
in terms of the vertically center of the first line of the label,
rather than the bottom of the first line of the label.  This change
allows a label to be precisely aligned with button text or an edit box,
which are positioned in a centering manner.  Label positioning remains
consistent with the previous system, just more precisely defined.

Make multi-line label[] elements work properly.  Previously the code set
a bounding rectangle assuming that there would be only a single line,
and as a result a multi-line label would be cut somewhere in the middle
of the second line.  Now multi-line labels not only work, but have
guaranteed line spacing relative to inventory slots, to aid alignment.

Incidentally fix tabheader[] elements which were being constrained to
the wrong width.

Given an unusually large form, in variable-size mode, the form rendering
system now chooses a scale that will fit the entire form on the screen,
if that doesn't make elements too small.  Fixed-size forms, including the
main menu, are have their sizes fixed in inch terms.  The fixed size for
fixed-size forms and the preferred and minimum sizes for variable-size
forms all scale according to the gui_scaling parameter.

There have been plenty of ppl involved in creating this version.
I don't wanna mention names as I'm sure I'd forget someone so I
just tell where help has been done:
- The partial android versions done by various ppl
- Testing on different android devices
- reviewing code (especially the in core changes)
- testing controls
- reviewing texts

A big thank you to everyone helping this to be completed!

Separate element for tooltips. Delayed showing,
use global color or given ones.

Fix positioning of tabheader in order to be usable for scaling GUIs
WARNING: this changes position of current tabheaders, mods have to adjust!