Add date selector for feed summary histograms

[landonreed]

Issue

Trips per date (and service hours per mode per date) histogram only shows a subset of dates to account for the fact that some feeds span many years. It defaults to the first date of service, making it difficult to view dates for some other period in the feed.

Solution

Add a date selector for these histograms so that you can jump to different points in time rather than being confined to the feed start date.