gdk/Application: Add Viewport member variable
EventHandler: Require Resize/DragEvent callbacks
Merge branch 'develop-0.1.x' into develop-0.2.0
gdk/Application: Set viewport size on window resize
gdk/Element: Implement Drawable
TestEngine: Implement new Resize/DragEvent callbacks
Merge branch 'develop-0.1.x' into develop-0.2.0
gdk/Application: Internal methods to get config width/height
gdk/Application: Method for disabling depth test

Also removes DEPTH_BUFFER_BIT from ClearFlags
gdk/Application: Whitespace fix
BezierCurve: No longer set point size in Draw
gdk/Application: Add TODO for main.config is a directory result
Window: Add Get/SetSize methods

Width/Height are cached as member vars. Might change this since GLFW gives
us API to retrieve these values.
Build: Add internal headers to project files
Merge branch 'develop-0.1.x' into develop-0.2.0
Add BufferList class
Shape: Inherit BufferList
Mesh: Factory function catches constructor exceptions
Cube: Factory function catches internal exceptions
Rectangle: Factory function catches exceptions