Debug|libdeng2: Describing rules as text

Added descriptions for rules so it is easier to see if there are any
mistakes in them (e.g., missing edges of a rectangle).
libdeng2|Counted: Added new variants of holdRef()
Fixed|Models: Possible out-of-bounds uses of the submodels array

In various places of the code there is an assumption that submodel #0
always exists. This may not be the case.
Fixed: Warning about uninitialized variables
Debug|libdeng2|OperatorRule: Improved description
Games: Added notification about added new games
Refactor|Client|UI: Added "ui" namespace for UI related enums and defs

The widget classes are not supposed to be in this namespace, though.
Client|UI: Added colors for LabelWidget and a missing function
Client|ScrollAreaWidget: Setting content size using rules
Client|UI: Added MenuWidget and a game selection menu

The game selection menu is a work in progress...
Fixed|GuiWidget: Blurring and alpha

The blur must be flattened before rendering it back to the frame
buffer.
Merge branch 'master' of ssh://github.com/skyjake/Doomsday-Engine
Default Style: Added logos for game plugins

Temporarily borrowed the old ones from Snowberry.
libgui|GLState: Normalized scissor

The normalized scissor is relative to the viewport, so it can be used
with downscaled viewports.
Client|UI|GuiWidget: Use normalized scissor for content clipping
Client|ButtonWidget: Visual tweak to button frame
Client|Console: Log background blur can be disabled, eat mouse clicks
Ring Zero: Improved game selection menu

Instead of opening the console, ringzero now shows a graphical menu
for selecting the game.