[MAIN FUNCTION] File upload added.

TODO:
- [ ] Add a confirm dialog for deleting the extension.
- [ ] Update the PR (probably I'll do it tomorrow).

You can check my new fixes: now the extension is ready to upload zip files and install them!
I've deleted 'tree' functions as I think they won't be in the final release and the main function is done (no need for testing).

Only wait until tomorrow. =)