Cleanup|Client: Macro naming convention (DENG_ instead of LIBDENG_)
Cleanup: Further cleanup after dropping Qt 4.6 support
libdeng2: Added methods to the Rectangle template
libdeng2: Added an easier way to get the appClock's current time
libdeng2: Method for checking if an Observers set is empty
libgui: Added template for new classes

Based on the never-implemented Window class.