Add ftw.labels filtering support to catalog source.

`ftw.labels` has a filtering feature, adding `labels` to the tabbedview request (as tabbedview property).
This change merges the `labels` value into the catalog query.
It adds a dict of allowed indexes to normalizer / pre processors, allowing to easily add more such use cases and pre process the values using a callback before merging it into the query.

This adds support for `ftw.labels` to all catalog source based views, without further changes needed.

@maethu can you take a look at it?