Fix issue2551029 (Jinja2 template install error) by deleting config.ini from all templates. Looks like classic and minimal never included a config.ini. Presence of config.ini stopped 'roundup-admin install' from generating an up to date config.ini. Created special option class for backend database. Comment now uses roundup.backend.list_backends to give user indication of valid values. Also we now get an error if user specifies invalid backend. Moved backend setting to top or [rdbms] section. It is the most important thing in there and if set to anydbm (or some other non-rdbm) the rest of the settings can be ignored. Change rdbms config section comment to indicate that the backend setting was used by other database backends. (e.g. if set to anydbm).

#!/usr/bin/env python

# Roundup requires Python 2.7+ as mentioned in doc\installation.txt
from __future__ import print_function
VERSION_NEEDED = (2,7)

import sys
if sys.version_info < VERSION_NEEDED:
    print("Content-Type: text/plain\n")
    print("Roundup requires Python %s.%s or newer." % VERSION_NEEDED)
    sys.exit(0)