Config per site

[knyjoh]

Now there is a config file per server, but it is desirable to have some configurations per site level.
It could be stored as a json-blob in the database on the site table.

Example of configurations needed:

• Selection of authentication methods to allow
• (Whether to activate ratings functionality or not) - future setting
• (Whether comments need to be approved before they're published) - future setting

[sirn-se]

The authentication selector was dropped, as it introduced problems without obvious solutions.

The framework for site-level settings is implemented and merged, with some basic settings as show avatar, newest/oldest first.