Datefilter map: Date filter enhancements

[gregallensworth]

Per chat today, the datefilter map's timeslider could use some improvements:

• [x] Apply filter only when Apply button is clicked; current change handler updates too aggressively, and "feels clunky" when one is updating the dates, e.g. in the middle of entering new dates one enters a range of "2008-01-01 to 2000-01-01" momentarily.

• [x] Existing calendar widget allows one to select a year, but that's not obvious: one must mouse over the year to discover this. Can this behavior always be in place so folks can find it?

• [x] Add UI below the date boxes, to go forward or backward 1 year and forward or backward 10 years. This would adjust both dates, "shifting the window" with one click.

[gregallensworth]

About 1 time in 4 on this PC, changing the date results in an endless loop of the map and the URL bar chasing each other back and forth, waffling between two dates.

To replicate, just try to pick a new date. Try it a few times. It will happen eventually, though it never did this in my earlier testing...

I expect that this comes from both the date filter control and the URL hash both trying to be the source of truth as to the map's date view.

• Changing the date filter UI will update the map. Updating the map changes the URL string.
• When the URL string changes, the URL hash params are applied to the dater filter and to the map. Thus, the URL string will update...
• I suspect that part of the problem is that applyUrlHashToMap() does the date filtering in a setTimeout so as to work around bugs in Mapbox GL API (it fires load before the map is fiully loaded).