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

* Add key settings to setting table and ignore them later
  This way they are added to the auto-generated minetest.conf.example
* Add flags type
* Add input validation for int, float and flags
* Break in-game graphic settings into multiple sections
* Parse settingtpes.txt in mods and games
* Improve description for a lot of settings
* Fix typos and wording in settingtypes.txt
* Convert language setting to an enum

According to its man page, the function gettext(3)
"may return a nonempty string" when msgid is "".

This commit fixes a bug where the comment ""
for some settings caused gettext to return a
"nonempty string", in this case header info of the
po file.

Settings are automatically parsed from builtin/settingtypes.txt
The edit dialog automatically adjust based on the type of setting

The Irrlicht engine supports antialiasing, and Minetest already supports
saving an antialiasing setting in its configuration file.  However,
Minetest lacked UI elements to set this setting, and previously the only
way to enable the feature was by hand-editing the configuration file.

Add a drop-down menu that can enable antialiasing.

This reverts commit 7b17b905.

Fixes issue with direct3d(8|9)

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!

Fix crash on using cursor keys in client menu without selected server
Add support for non fixed size tabviews