[FEATURE] Integrate datesearch

[michaelkubina]

This PR integrates a datesearch, that can be activated within the search plugin and will be displayed on the website. When activated it presents two input fields for dates, so the users can input a range if necessary. When a datesearch was performed both the sorting form and the facets will recognise it and apply the filterquery as well. The filterquery is a simple range search (via join query parser over the uid) on the new mandatory solr-field "date". All language localizations have been applied.

This feature allows for an easy and convenient date-range search in any collection for all objects that have dates, e.g. in a newspaper-collection.

[sebastian-meyer]

Thank you for your contribution!

Please see my comments below and please resolve the merge conflicts.