As noted in https://github.com/hypothesis/h/pull/3284#issuecomment-219031557
threads which have been explicitly collapsed need to have their
expansion state reset when the filter query changes.

This commit resolves this by moving the search query and sort UI state
into the annotationUI Redux store and handles the state update
in a SET_FILTER_QUERY action.

This means that the rootThread module no longer maintains any primary
state of its own, just state derived from the current annotationUI
state.