Made fps members volatile

Those members get reset from UI thread.
Updated description
Show all available values in comments
Use uv instead of p
Improved performance for mobile GPUs
New icon
Renamed duplicate for clarity
Updated comment to be more verbose
Get fps view every time anew instead of saving it

It's better to not save the view returned for R.id.fps because it's
impossible to know when Spinner does change the selected view; especially
when the adapter changes which may update the spinner not immediately.

Anyway, getSelectedView() and findViewById() are just lookups and this
method is only called every ShaderRenderer.FPS_UPDATE_FREQUENCY milliseconds
and if fps did actually change so that shoudln't be problem
Made highlighting colors constants
Fixed loading of missing shaders

If a shader isn't available anymore choose another one at random.
Added method to get a random shader
Set values only if locations are found