Switch away from fatfree for database

[jtojnar]

Slowly tearing fatfree out of the codebase.

We should probably wait for after 2.19 so that we can use stuff depending on newer PHP.

Alternatives:

• dibi
• https://packagist.org/?query=pdo

See also:

• Do not use F3 for configuration management #1261
• Use a better translation library #1084
• Switch away from fatfree for routing #1265

[jtojnar]

This was done in e71194b.