Sort out handles for fine searching in time filters

[visead]

I'm bumping up the priority on this as we are getting some potential user questions.
We need a solution to selecting narrow ranges of time on the time facets (geochronology, analysis entity ages):

A use case is that someone in Finland wants all samples dated to around 4200 BP, and just now we can't zoom in with fine enough resolution.

I liked the manual input boxes we had in a prototype...