Blender Git Loki

Updated and extended Regression Testing frameworks (Gsoc 2020)

This revision contains the following changes-

- Updated the existing testing framework for Modifiers for Regression
Testing.
- Tests for Physics modifiers and remaining Generate and Deform modifiers are added.
- The existing `ModifierSpec` is updated with backward compatibility to support Physics Modifiers.
- Now there is support for frame number and giving nested parameters for attributes.
- Some Deform modifiers required Object Operators, e.g. "Bind" in Mesh Deform, so a new class was added to support that functionality.
- A separate class for holding Particles System, they are tested by converting all the particles to mesh and joining it to the mesh they were added.
- Updated the format to add tests for Bevel, Boolean and Operators as
well.

Reviewed By: zazizizou, mont29, campbellbarton

Differential Revision: https://developer.blender.org/D8507