feat: creating, copying & moving in folder_browser

[fdschmidt93]

Closes #78

This commit enables creating, copying, and moving
files and folders from within folder_browser mode.

In doing so, the currently selected directory within
folder_browser serves as the target directory for the
corresponding telescope-file-browser action.

[fdschmidt93]

@ikerurda would you mind testing that

1. Copying, creating, moving files in file_browser mode works as you'd expect from current things
2. Copying, creating, moving files to the currently selected entry of the folder browser works as expected?
3. Copying a selected directory in folder browser should trigger that folder browser exists and that you can create a copy with a different name

That would be very much appreciated :) I've tried it once, and after I fixed that copying a selected folder in-place leads to recursively copying, I think it's good 😆

E: I also need to mark new behaviour on the README then.

[ikerurda]

LGTM, and very cool!

Maybe we should add the destination path to the confirmation message, that would make it clearer.
What do you think?

[fdschmidt93]

Thanks :)

Do you mean the target_dir? name is already printed. I agree that can be improved, but I'd merge now as state-of-things suffice and will revamp messages/notifications eventually ideally via #72