Added property class

Added property class which contains a key and value as strings, and
subclasses which allow explicit types within these properties.
Functionality to write properties to and read properties from config
files is next on the list.
Doxygen integration

Finished documenting the code so far using Doxygen (whew).
Added "property variant"

Calling passTo on a property with a property variant parameter will
return the value of the property as the correct type, contained inside
the visitor. This allows you to retrieve a typed property from a base
class pointer without having to re-cast the pointer.
Added OpenGLWidget and Viewport2D

Began implementing OpenGL support (removed GLEW because it turned out I
just had the wrong version of Qt Creator). The Viewport2D class is
intended to be fleshed out into a class that will render 2D graphics
such as the grid views.
Merge pull request #2 from x6herbius/workbench

Workbench