Update counts/language when filtering by last state change

[RyanFrantz]

When a user opts to filter hosts/services by last state change, the totals and language on the dash should be updated to reflect the filter results.

For example, if only 4 hosts and 10 services changed state in the last 15 minutes, the totals should be updated with those counts, by state, and the language around the header blocks should clarify that the results are from the last n time period (i.e. 4 hosts have changed state in the last 15 minutes; There have been 0 failed services in the last 1 hour, etc.).

This is tidy up work related to #47