Add messenger.getFilters() to get the number of active filters.
Use the full dataset, but only update the timeline if a filter is set.

The full dataset is much larger. Mongo's aggregation can't handle all of it,
but most sensible filters will reduce it to something that Mongo can
respond to in a short time, assuming proper indexes are in place.
Use Tangelo Geomap's message to update the geographic bounds

Tangelo's bounds are updated by Aperture Tiles' message, but then the
user can move around within Tangelo, so it is important to update in
response to those messages.
Handle user selection in Geomap and Mentions
If an empty user is specified, remove the user filter.