Game class is too huge and has too specialization on various subjects, like UI, formspecs, client, renderer. Start to move UI related things to GameUI object and cleanup them
Other improvements:
* updateChat: more performance on error messages by remove string copies
* Initialize all game class members in definition instead of constructor (with nullptr instead of NULL)
* Drop unused Client::show{GameChat,GameHud,Profiler,GameFog}
* Add GameUI unittests
* Add Device3D class which will contain IrrlichtDevice interface
move getSupportedVideoDrivers to Device3D
Add Device3D singleton & use it in various places
Rename Device3D to Rendering engine & add helper functions to various device pointers
More singleton work
RenderingEngine owns draw_load_screen
move draw functions to RenderingEngine
Reduce IrrlichtDevice exposure and guienvironment
RenderingEngine: Expose get_timer_time() to remove device from guiEngine
Make irrlichtdevice & scene manager less exposed
* Code style fixes
* Move porting::getVideoDriverName, getVideoDriverFriendlyName, getDisplayDensity, getDisplaySize to RenderingEngine
Fix XORG_USED macro -> RenderingEngine + create_engine_device from RenderingEngine constructor directly
* enum paralax => enum parallax
* Move KeyList & InputHandler from game.h to client/inputhandler.h
We have a header for inputs, move inputhandler class & related keylist object to it
Also introduce a cpp file for MyEventReceiver::OnEvent function in inputhandler.h because a so huge function doesn't needs to be inlined
* Pass clang-format on inputhandler.{cpp,h} (compatible)
* Combine client and server man pages.
* Update unit test options and available databases in man page.
* Add `--worldname` to man page.
* Fix a bunch of places where `"Minetest"` was used directly instead of `PROJECT_NAME`.
* Disable server build by default on all operating systems.
* Make `ENABLE_FREETYPE` not fail if FreeType isn't found.
* Enable LevelDB, Redis, and FreeType detection by default.
* Remove the `VERSION_PATCH_ORIG` hack.
* Add option to search for and use system JSONCPP.
* Remove broken LuaJIT version detection.
* Rename `DISABLE_LUAJIT` to `ENABLE_LUAJIT`.
* Rename `minetest_*` variables in `version.{h,cpp}` to `g_*`.
* Clean up style of CMake files.
