Change command to run on download finished event

When a download completes first close the torrent then move the files
around then start the torrent again. The previous method of simply
moving the file downloaded by the torrent was throwing errors in the
newest version of rtorrent from homebrew.
Refactor muttrc files

Extract common settings to `config/mutt/muttrc` and source it in each
.muttrc file for individual accounts.
Move colorschemes into new themes directory