* 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
* Optimize updateFastFaceRow processing by removing some TileSpec copy
It permit to decrease this function from 54% runtime to 45% and reduce copy from 14% runtime to 12.5%
getTileInfo also reduced from 27% to 23%
* makeFastFace should use a const ref too
this trigger a const pointer need in the underlying function
Also fix some code style and prevent calculating 4 times the same position at a point
* Reduce a comparison cost for lights in updateFastFaceRow
