Collection filtering

[bastianjoel]

Currently the results are sometimes bad because on the client side it is possible to filter for collections but the results returned by the service are limited to 100. This in some cases results in much less results than available. In some scenarios this also makes searching for meetings impossible.

It should be possible to pass collections by a query parameter. Also in the search.yml a new collection attribute contains should be added which indicates which additional collections can be found within a model.