This commit moves the API of selecting faces, vertices and edges to a DRW manager engine.
Reviewers: campbellbarton, fclem
Subscribers: jbakker, brecht
Differential Revision: https://developer.blender.org/D5090
- use DRW_engine prefix for engine types.
- use engine suffix for files that define a draw engine.
- remove engines from include path (they're only referenced once)