These shouldn't be there anymore since the plugins have been deleted

authmysql and authpgsql were replaced by authpdo two releases ago.

shorter names are more in line with what we already use, makes less
layout problems in the documentation and is easier to type when telling
people about it.

This adds two new config options:

`search_limit_to_first_ns`:
Limit the search to the current X namespaces. When a search is executed
from a page within a deeper namespace, the first X namespaces will be
added as filter.
Possible use case could be with language namespaces to ensure that the
default search is initially within the current language.

`search_default_fragment_behaviour`:
Option to specify the default fragment search behavior

The goal is to make the css replacement accessible in other contexts,
for example for the manifest.