Add mutt_oauth2.py command line parameters

This extends mutt_oauth2.py with more command line parameters to avoid the necessity of 1. patching the script and 2. answering interactive questions. The documentation is also updated to reflect this change.

Anybody prefering the old way is of course still free to hard-code the gpg and other IDs in the source code. If the command line options for the --authorize mode are not supplied, the script falls back to the interactive mode as before.