[FEATURE] Add an Upload interface

[pryrt]

Currently, the plugin will just do downloads (from Repos to the local machine)

It would be nice to also allow uploading a UDL and/or accompanying AC/FL, or a Theme, to the Collection. Things that would need to be implemented/researched to allow for this:

• Code:
  • Separate dialog which enumerates all the UDL/etc on the local PC and allows for upload
  • Submit PR (if possible, per research)
• Research:
  • Learn how to use GH API to submit a pull request
  • Can it be done using user's email if they have a GH account?
  • Can it be done using user's email if they don't have a GH account?
  • Do they need to have a fork and/or a branch to be able to submit a PR?