Better selection of bounded edges + boundary edges

2 Major changes: 
- Replaced shortest_path_select for doing a partial/bounded edge loop or partial edge ring selection with code from Loopanar: https://sourceforge.net/p/blendamajigs/wiki/Loopanar/
- Added ability to double click on a boundary edge (open hole in a mesh) and select the "loop" of all connected boundary edges. (For now only up to 1000 edges as a safeguard; will probably change later.)

Author: MightyBOBcnc