[search bar] subparagraph grouping

[schloett]

Allow to filter the generated query by subparagraphs and corresponding main topics. Current filters are 'all', 'persons' and 'locations'. Especially for long paragraphs, it would make sense to provide sub-queries for the sub-paragraphs. This might be realized by adding the main topic of the sub-query to the filter set. However it needs to be checked if the main topic is the right choice for this filter, since it might be the same for all sub-paragraphs.