libdeng2|Performance: String memory allocation behavior in formatter

Reserve memory for the line in advance when filling tabs.
libappfw: Added DocumentPopupWidget

Simple combination of a popup with a document widget inside. Useful
for many simple info popups (e.g., console autocompletion popup).
libgui|Client: Improved handling of indents in text drawing

Indents can be marked and reseted individually.
Refactor|libappfw: Use DocumentPopupWidget
libappfw: Widget improvements

MenuWidget’s layout can be modified by outsiders (non-const accessor).
Ensure only the main thread creates widgets in ChildWidgetOrganizer.
PopupWidget doesn’t extend beyond the top of the view when opening.
ScrollAreaWidget’s child clipping can be disabled.
Refactor|UI|Client: Use DocumentPopupWidget
Refactor|Game: Added a method for getting a text description

The same information that is printed with ‘inspectgame’.
UI|Ring Zero: Improving the game selection menu

Added additional buttons beside each game to access further
information (later, settings) about the game. Removed the
game authors from the menu to avoid clutter (full descriptions
in the info popups).