Moved password promting into imapserver.py. Passwords are now asked
for on-demand and typos will no longer crash the program (the user
will be re-prompted). Closes: #162672.
- Moved some code from offlineimap/init.py to new file
offlineimap/syncmaster.py to help dileneate between code that
performs different functions.
- Moved threadexited from offlineimap/init.py to
offlineimap/threadutil.py.