Cleanup|Client|Server: Removed con_bind.h (obsolete)
libdeng2: Added Action, a base class for UI actions
libgui: Cleanup
Refactor|libshell: Derived shell::Action from de::Action
Refactor|Client: Added InputSystem, CommandAction, WidgetActions

InputSystem is a System that governs the input devices and produces
input events.

CommandAction is an Action that executes a console command when
triggered.

WidgetActions is a database of actions bound to specific widget(s) /
binding contexts (transitional component).