Client|libdeng2|Script: Separated app-specific stuff out of Config.de

The application-specific "appconfig" module is now responsible for
the default configuration of the application (window, console, etc.).
UI|Client|ToggleWidget|Default Style: Tweaked appearance and animation
UI|Client|VariableToggleWidget: Added widget for toggling script variables

Syncs the value of a script variable (boolean) with the on/off state
of the toggle widget.
UI|Task Bar|Refactor: Use VariableToggleWidget for the FPS counter menu item

There is now a proper widget that makes it easier to implement the
FPS toggling (via Config.window.main.showFps).
UI|Client|Console: Added option for scrolling log to bottom on Enter

Using a VariableToggleWidget in the [>] menu.