Ability to filter images shown by time uploaded

If we allow people to see each others' images, filtering what's shown by timeline is going to be very useful. Luckily there are a range (pun intended) of options for this:

• https://github.com/svitkin/leaflet-timeline-slider/
• https://github.com/socib/Leaflet.TimeDimension
• https://github.com/dwilhelm89/LeafletSlider
• https://github.com/skeate/Leaflet.timeline

My ideal is to have a timeline slider with start/end handles to show only those images which were created/uploaded in the selected time range.

This could start with just hiding in the UI, but we might eventually try to wire this up to an API call that fetches within a time bounds. But that can come later.