Switch out the filtering interface for a single search box with a small query language

[robx]

Thinking of a more search engine-like interface:

heyawake yajilin source:twitter solved -broken -variant -author:fdsa

This would allow stripping down the query part of the interface significantly while expanding the possible queries (if done right).

Some issues:

• discoverability of type names (and ideally we'd allow searching for any type aliases, e.g. bag vs corral vs cave); this would require backend changes
• discoverability of author names (ideally typing author: would pop up some kind of author query interface)