Core: contextual tag search

[andykais]

Searching by tag should also allow passing in a list of tags to filter by ({media_containing: {tags: 'foo'}}. The tag search should be able to filter out tags that have no media associated with the media_containing filter

[andykais]

related to this, we should pass along tags that should not be part of the results (e.g. I already searched for "foo", so exclude "foo" from the results of "f"