checks that config.txt compatible with running offline

- checks that database is using sqllite rather than mysql (although mysql could in theory access a local mysql DB, in principle seems simpler to recommend "development" mode use the local sqllist db
- checks that server host is set to localhost (works even when offline/no ip)
- otherwise prints a suggestion about how to fix these things and quits.

note: it might be more user-friendly to change these things temporarily for the user but i'm hesitant to go around changing people's config.txt file without them actually requesting it via the command line.  perhaps better to help people understand and change it themselves.