Client|UI: Added DocumentWidget for larger blocks of text

While LabelWidget is good for small static UI texts, DocumentWidget
is designed to handle longer texts that typically are only partially
visible.
Client|UI|DocumentWidget: Working on drawing text
Task Bar|Console: Adjusted 'taskbar' command behavior when task bar open

If the task bar is open but the command line is unfocused, 'taskbar'
will set focus to the command line rather than closing the task bar.
Only when the command line is focused and the task bar is open, the
command will close the task bar.
libgui|GLState: Added missing assignment operator
Fixed|FontLineWrapping: A double newline stops wrapping operation
Client|UI|ScrollAreaWidget: Indicator origin, geometry updates

When the indicator is animating, geometry update requests occur
automatically. Also it is now possible to define the origin for the
indicator geometry.
Client|UI|GuiWidget: Added method for calculating normalized content rectangle
Client|UI|DocumentWidget: Finished basic implementation

DocumentWidget now allocates and draws only the visible range of lines.
Clipping is applied to the drawn text. The scroll indicator is included
in the background vertexbuf.