Resolve many of Phabricator's setup issues

Those that remain:

- no sendmail binary found
- server timezone not configured
- upload limit not yet configured
- base URI not configured
- no authentication providers configured

These are easy enough to do at runtime, and given their site-specific nature
may be better to do so.
I don't really know. I'm just doing [what phabricator suggests](https://github.com/phacility/phabricator/blob/master/src/applications/config/check/PhabricatorSetupCheckMySQL.php#L134).