Change the way ads are queried

This changes the way ads are queried to accomplish three goals:

* better search matching
* show the correct number of ads per item in filter (categories, types, regions)
* order the results by search score instead of publish date when searching 

Instead of using the database it now relies fully on SOLR for search and faceting.

Things to do:

- [ ] cover it with specs
- [ ] configure SOLR for Croatian