Option to easily open the meshswap file

[TheDuckCow]

Likely leveraging the built in linked library addon (and prompting users to enable it, if not found), make it easier and faster to open and edit the Meshswap source file for edits.

This should be weighed against the fact that user edits of the meshswap file will be reverted if they ever update in blender to a newer MCprep release.