Instead of passing a `searchController` prop into `TopBar` which is
responsible for reading and updating the search query, from different
sources depending on whether this is the sidebar or stream, handle
reading/updating the search from within `TopBar` itself:

 - In the sidebar, read/update the filter query in the store
 - In the stream, render a `StreamSearchInput` control which
   reads/updates the "$q" param from the Angular `$location` service

This removes some indirection and makes it easier to follow where the
search input gets its data from and what happens when it is changed.

Also fix a bug where existing annotations were not cleared after a route
change from `/a/:id` to `/stream?q={query}`.