[Client] A better way to do media mapping, stills gallery, proxy media, etc...

Currently, Resolve requires a restart after each change of the media mappings (Preferences > Media Mapping). This feature is pretty crucial for distance collaboration - to ensure two users don't have to keep relinking every time they come into the project.

- The media mappings are stored in the System preferences file `/Users/jonnyhyman/Library/Preferences/Blackmagic Design/config.dat`, which is just plain text, so can be modified on the fly.

- The first one in the list is used to store gallery stills and cache files, but those directories are not shared between machines, generally

The real question is how to force Resolve to update media mappings without restarting Resolve...