pingo. Minor fix to gl object is valid

Move the test if the gl object is null to the base gl object.
Derived object implementation only test that the handle is of the correct type.
pingo. Simplify render object code.

Remove the gl uniform func, gl uniform will call the gl uniform function directly in execute.
Only declare the gl uniform interface in the render object header. Move the gl uniform impl to the source file.
Render object initialize creates the gl uniform directly and not through a factory method.