Extend the search grammar

[critocrito]

The current search grammar contains the following elements:

• free search based on OR connections, e.g. term, term other-term or "phrase to search.
• selection of tags, i.e. tag:my-tag.
• selection of sources, i.e. source:youtube_video

The search grammar should be extended:

• general exclusions, e.g. -tag:my-tag or -source:youtube_video
• has a type of media, e.g. has:video or has:video
• search through annotations as well.
• boolean sets, e.g. term1 AND term2 NOT term3