Fixed|libappfw: Colors with inverted Aux Button and Button styles

AuxButtonWidget was not correctly managing the text/border of its
buttons. ButtonWidget was also not restoring the right color if the
color was changed during a Hover state.
libgui|PersistentCanvasWindow: Saving and restore state during runtime

The window can now remember or restore its state at any point without
touching the Config.
Documentation|libcore|String: Added comment about default codec
UI|Home: Revised contents of saved game menu items

User-given title on top, however now comes with a "tag" saying
'saved in (game)' that is visually different than the game identity
keys in the normal game selection menu items.
UI|Client|AudioSettings: Select soundfont using native file picker

Added the class CVarNativePathWidget (based on aux button) for
choosing a native file.

IssueID #1907
libappfw: Improvements for widget background blurring

Instead of each and every transparent widget doing a full redraw of
the entire view for the blur, now the Style can provide a common
source for the blurred background. This can improve rendering
performance significantly.

Added a GuiWidget attribute that allows a widget to draw its blurred
background into a texture even though the widget itself is not
visible.
UI|Client|Performance: Reduced redundant background blurring

The client window already has a task bar blurring widget that gets
used during the tutorial. The same blurred content is now used in
Ring Zero for all widgets that have a blurred background.

In the future, the same can be done when a game is loaded, when game
rendering is more optimized for less redraw overhead.
UI|Home: Tweaked font styling
libappfw|GuiWidget: Added blurred background with a solid fill

Also added a new attribute that makes the opacity of a widget
independent of its ancestors.
UI|Client|Home: Added a background for the game filter area

The sort order and filter tabs conflict with the menu contents when
the menu is scrolled up. Now there's a white blurred background
that appears behind the top part of the view when the menu is
scrolled.
Merge branch 'master' of ssh://github.com/skyjake/Doomsday-Engine