Abilities Bar

Reimplemented the abilities bar.

The abilities bar shares behaviour with the party bar; an outer frame
which responds to the mouse cursor, an inner frame which reflects which
ability is currently selected, and an icon representing the ability. The
abilities bar is visible when only one player party member is selected.

The GUIManager function XhitYforZ now takes a string argument in place
of the bool, which represents the text between [X] and [Y] in the
message. Added a combat log message for healing done.