Merge pull request #25 from Tectu/master

Merge Tectu Changes
Create generic GWIN Draw routine

For some GWIN controls they support a Draw() routine.
For those controls the base class now supports a generic Draw routine
which will call their specific Draw routine.
The only GWIN's with a Draw routine currently are Buttons and Sliders.
Merge pull request #59 from inmarket/master

Generic GWIN Draw routine