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