libgui: Added Window base class, synced version with project version
Refactor: Preparing to move Window to libgui

It will serve as the base class for CanvasWindow.
Mac OS X: Dropped support for OS X 10.4

Also means Carbon Qt (4.6) is gone as well as PowerPC builds.
Builder|Mac OS X: Prevent building on OS X 10.5 (targeting 10.4)

The autobuilder will now skip 1.11+ builds on OS X 10.5, which has
been used for building 10.4+ packages.
Refactor|Client|libgui: Started revising window architecture

Began a large refactoring where the window architecture is
"re-imagined" with proper separation of concerns, and generic portions
are relocated to libgui. Hopefully after this window management is
finally up to Doomsday 2 standards.

In this commit DisplayMode, DDKEYs, and the persistent window state
management have been moved to libgui. Canvas's mouse and keyboard
event production has been abstracted behind Mouse/KeyEventSource,
so that instead of events they produce notifications.

Note: Not finished at all -- barely compiles on OS X, likely fails on
other platforms.
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.
Documentation: Instructions for adding new versions of public APIs
libgui|X11: Use "x11" as a platform suffix
libgui|Canvas: Cleanup and debug log messages
libgui: Working towards a successful build on Windows/Unix
Documentation|API: Cleanup
libgui: Cleanup
Refactor|Client: ClientWindow implemented, added GuiRootWidget

The ClientWindow is the highest-level window class that manages the UI
widgets in the window.

GuiRootWidget is the root widget that is used inside a ClientWindow.
libgui: Cleanup and post-refactoring fixes
Refactor|Client: Use new ClientWindow class, WindowSystem methods

Moved window management methods to WindowSystem.