Adds initial ingame gamepad support to minetest.

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

* Move key types into own file
* Use Generalized input methods in game.cpp

We can remove the function in MtNativeActivity now
as it serves precisely that purpose: to tell irrlicht
that we handled the esc key.

TODO for later:
 * Perhaps try to find a more performant container than KeyList

Enable the server to request the client to reconnect.

This can be done with the now extended minetest.request_shutdown([reason], [reconnect]) setting.

This removes a lot of narrow/wide conversions where a wide string was never used.

The following is a record of 31 commits before squashing:

Revert "Remove m_ext_ptr in GUIFormSpecMenu, replaced by refcount mechanism"

This reverts commit b49e5cfc.

Basic reformatting with astyle
-- additional formatting will be modified, manually, as the need for it is encountered

Start "outlining" what a MinetestApp class might look like

Add MinetestApp::shutdown()

Converted class member functions to camelCase and created protos for new functions

First stage of connect to server done

Add get itemdefs/nodedefs/media code

Init clouds, camera, sky, init GUI, HUD

Input handling

Client events, camera, sound, draw

Fix wield hand getting stuck digging and add debug text back

Fix FPS

Added profiler graph back

Fix FPS issue
Need to work out what went wrong and clean up the copy/paste stuff

Annotate

Various:
Rewrote limitFps()
Limited scope of some variables

Jitter calcs

Reduce scope of objects

Move some stuff out of ::run and minor formatting cleanup

Scope reduction

Function splits

Removed old (broken) limitFps()

Added exception handling back

Fixed some formatting

Reverted commented out unit tests (uncommented them)

Slow clouds down on loading and media screens so the behaviour is like the original the_game()

Formatting/style (no functional changes)

Manually reapply upstream b49e5cfc: Remove m_ext_ptr in GUIFormSpecMenu, replaced by refcount mechanism

Fixed silly errors on my part
Minor formatting cleanups

Removed strange differentiation in FPS limiting when loading
FPS limiting was done differently if cloud_menu_background was true, which does not make sense

Cleaning up

Add some comments

Switch the license to be LGPLv2/later, with small parts still remaining as GPLv2/later, by agreement of major contributors

Defaults modified from original: alpha=200, key=F10

This allows us to map the keys which are not considered in
irrlicht's EKEY_CODE system, such as \, [, /, ] etc.