exclude aggregator

This feature allows to exclude parts of a query when defining the result set used by an aggregator.

Based on: https://wiki.apache.org/solr/SimpleFacetParameters#Tagging_and_excluding_Filters

I work at a company that develops ecommerce solutions and we use the solr feature a lot to provide a better search experience while keeping the query size manageable. And the one excuse people gave me not to use elasticsearch was that this behaviour would be to verbose, having to write the whole query in each aggregator.
I love elasticsearch, and want to use it in future projects.

I experimented with a more generic approach which allowed to remove/cut a branch of the filter tree at any point,
but there were some inconsistencies in behaviour when excluding in a 'or' filter vs 'and' filter, because having a null for a filter is not treated the same way everywhere.