UI|Client: Replaced "Multiplayer Games" with a "Games" dialog

The Games dialog shows both the available game sessions and the
multiplayer games. It uses the same game selection widget that is
used in the Ring Zero UI.
UI|Task Bar: "Games" is only accessible when not in Ring Zero
UI|Client: Close Games dialog when a game session has been selected

A signal is emitted from GameSelectionWidget after a selection
has been made.
Fixed|libdeng2|Time: Printing the correct time
Refactor|libdeng2|Action|Counted: Actions are reference counted

Rather than requiring duplication of Action instances, they are now
reference counted so they can be conveniently shared between items
and widgets, and multiple widgets.

Added more convenience utilities for Counted objects: RefArg and
AutoRef. The former takes care of reference passing convention in
method arguments while the latter auto-releases a reference after
its scope runs out.
Refactor|libshell: Use reference-counted Action instances
Refactor|libappfw: Use reference-counted Action instances
Refactor|UI|Client: Use reference-counted Action instances