libdeng2|Widget: Added the behavior flag 'ContentClipping'
Client|Task Bar: Clear command line when dismissing console
Fixed|Client: Use the correct font when rasterizing text for GL drawing

The font used by the font line wrapping was not always applied when
GLTextComposer rasterized the lines.
Refactor|Client|Widgets: GuiWidget stores/updates common style properties

Also cleaned up colors.dei in the Default Style pack a little with
new gui module color operations.