Fixed|libgui: Clearing a Drawable

The default program was not cleared with the rest of the Drawable.
libdeng2|Animation: EaseIn and EaseOut functions were mixed up
Client|Widgets: Added BlurWidget

Simple utility widget for setting up a blurred layer in the UI.

Refactored GuiWidget's blurred background to allow other widgets
to draw a portion of it.
Fixed|libdeng2|ScalarRule: Shifting a scalar animation

The rule must be invalidated if it is shifted so that the new value
becomes effective.
Client|Console: Adjusted scrolling in LogWidget and ConsoleWidget
Client|LogWidget: Restored default background