Events UI: improve filtering + show user details + user network graph

[lukewendling]

fix #139

Tasks

• [x] show all tweets for selected event.
• [x] support regex for more robust search queries, and allow for case-insensitive searching.
• [x] clear search box (instead of page refresh) to revert filter.
• [x] show top hashtags in events list.
• [x] show selected author's other posts.

[lukewendling]