Support type-in values for time slider value, time slider limits

[rsignell-usgs]

I'm trying to work with this NEXRAD Weather Radar WMS for the US that has 5 minute intervals from 1995 to the present, so more than 2 million time values.

The WMS endpoint is:
http://mesonet.agron.iastate.edu/cgi-bin/wms/nexrad/n0r-t.cgi?service=WMS&version=1.3.0&request=GetCapabilities

The default time slider behavior in TerriaJS shows only the first 1000 values, which gets us Jan-Mar 1995. 😿

I could bump the "maxRefreshIntervals" up to 2,000,000+, as in
#1365 (comment)
but really the user would like to zoom into a particular 3 day storm, and play each 5 minute radar image to watch the storm develop.

So having the ability to type in a specific time, or type in start and stop values that would set the limits of the time slider would be a huge benefit.

I don't think this is quite covered in #984 :