Added initial EffectWidget implementation

The code runs, but the shader must be set manually.
Moved effectwidget example to separate file
EffectWidget: Implemented basic fbo effect stack
Improved EffectWidget, and updated example
Added new effects and improved example
Added new effects and fixed existing ones
Changed EffectWidget to use effect classes
Changed effects to use effect classes
Added initial effectwidget doc
Added effectwidget doc for effect creation
Added source property to EffectBase
Added AdvancedEffectBase
EffectWidget: Initial docstring run
Removed unused effect strings
Added/updates most docstrings to effectwidget module
Tidied all methods of the effectwidget
Set __all__ exports in effectwidget.
Fixed incorrect super call in AdvancedEffectBase
Miscellaneous fixes pointed out by tshirtman
Fixed AdvancedEffectBase inheritance