Visualize glacer termini (or other layers) over time

[MattF-NSIDC]

Requires major configuration schema changes – wait to see whether we're going to stick with Luigi before doing this!!!

@trey-stafford used a dataset recently (reviewing for MEASURES?) that worked perfectly with the temporal controller. If we can remember what dataset that was we could reference it in setting up our layers with time controller support and write some good docs on how to make the time controller happy.