Remove ambient

It's already added in the diffuse env pass
Update doxygen comment.
Port instancing shaders to singleton.
Try a fix for intel and kart selection screen.
xrandr: fixed issue with fullscreen window which was placed in wrong screen in some window managers.

In some cases main screen may have other position than (0, 0) - fixed it.
xrandr: now it seems to work fine. I enable it for testing.

This should be useful for people which have two or more display devices. It changes resolution only on main screen and leaves other screens untouched.

Currently I use screen which is the most on left (or on top). Ideally we should be able to choose in settings which screen we want to use. But support it on all platforms is rather too much of work. We could also detect from which screen STK was executed. This can be done differently on different window managers, but nothing impossible. Maybe in future.

Perhaps we should add fallback using old xrandr method.

BTW. in some specific cases it works better than SDL2 ;-)
Applied konstin's bugfix for an editor crash.
xrandr: add support for rotated screens
Use an header included in every shaders.
Forget a shader + remove shader output
Add screen fallback in case no ubo are here.
Ignore minor logging spammed by recent nvidia drivers
Disable shadows when UBOs are off
Fix previous commit about shadows vs UBOs, had forgotten shadows is an int and not a bool
more video settings fixes
Add option to randomize particles start position, and use it on snow, so that snow falls more evenly
Try to fix too dark tracks.
Fix strange colors in rtts.
bugfix, only use the texture in layer 0 to apply material
Get dimensions of best resolution before creating irr device.

I also changed default 800x600 resolution to the size screen because sometimes this resolution may not exist. For example in rotated screens.