New filter type "distinct" for the livetable

This type of filter will restrict a select list to options that match, for a field, possible values in the current filtering state.

For example, if we make the field "doc.space" of such type "distinct" in the AllDocs table, and that the current filtering state brings document only in spaces "XWiki" and "Panels", the filter for doc.space will only propose those 2 options.