Refactor|Optimize|libdeng2|libgui: Enhanced BitField behavior

de::BitField is heavily used for managing the OpenGL state in
de::GLState. However, it was storing the elements metadata separately
in each BitField instance even though the metadata is the same for
all the BitFields used in GLState, and every time a BitField was
copied it was necessary to make a copy for the metadata and destroy
the old copy. This produced a measurable overhead when doing lots
of GLState::apply() calls.

Now BitField stores the metadata externally and it can be shared
efficiently by multiple instances.
Merge branch 'ui-multiplayer' of https://github.com/skyjake/Doomsday-Engine into oculus-refactor
Fixed|libcommon: Compiler warnings (missing braces around initializer)
UI|Ring Zero: Game Selection menu layout

Take into account the height of the game filter in the top of the view.
Merge branch 'master' of ssh://github.com/skyjake/Doomsday-Engine into ui-multiplayer
libappfw|LabelWidget: Added special "separate" align mode for labels
Refactor|libappfw|Client: Fluent interface for widget Margins
libappfw|FoldPanelWidget: Adjusted fold indicator placement
Fixed|Resources|Client: Setup of ID'd 3D models (missing particle/sky models)
Refactor|libcommon: Continued replacing logical map indices with Uri

Also renamed various top-level game functions to standardize naming
wrt game session management.
libappfw|LabelWidget: Added overlay image drawing for labels

The "separate alignment" mode turned out to be infeasible, because
when used, the label should be manually sized rather than using
an expanding policy. This would have complicated the internal logic
of the widget too much.

Now labels can have a simple overlay image drawn on top.
UI|Client|libappfw: Adjusted fold panel indicators

Also, aligning the Reset buttons of the Renderer Appearance
sidebar vertically with the fold indicators.
Merge branch 'ui-multiplayer'
Fixed|X11: Getting GL extensions and changing window size
Merge remote-tracking branch 'origin/master' into oculus-refactor
Fixed|Unix: Crash when launching application (UnixInfo)

UnixInfo needed to know the application's /etc path, but the application
had not been fully constructed at the time.
UI|Client: Added "24-bit" color depth to Video Settings