Blender Git Loki

Initial implementation of Shader FX (effects).

Now, the FX are used only by grease pencil object, but the design is ready to be used for other object types.

These FXs replace the old VFX modifiers, that were removed during the first steps of the greasepencil-object merge review.
The new implementation is fully separated of modifiers and with its own management modules.

Differential Revision: https://developer.blender.org/D3513