Shell: Added a stub for the Shell application and shared lib

The Doomsday Shell is a tool for running and monitoring a dedicated
server. It has both a GUI/Qt interface and a text-mode, command line
interface.

See: http://dengine.net/dew/index.php?title=Refactor_engine_into_a_shared_library
Shell: Basic GUI app stub

Created an empty main window.
qmake|Mac OS X: Attempting to fix 10.4 build

At least need to link with HIToolbox.
Server|Mac OS X: Fixed Mac OS 10.4 build
Fixed|Console Renderer: GL_TEXTURE stack underflow with con-background-turn

If both a console background material and a non-zero turn velocity
was configured, the GL_TEXTURE stack was manipulated incorrectly,
resulting in underflow.
Merge branch 'master' into revise-texture-animation