Blender Git Loki

Fix T62104: VertexGroup.add() doesn't push depsgraph update for the mesh.

When adding and removing weights from the python api, no depsgraph
updates were triggered. This would cause the mesh geometry to be out of
sync in the viewport if there were any modifiers that used the vertex
groups in question.

Reviewed By: Brecht

Differential Revision: https://developer.blender.org/D4439