Placefile endpoint(s) for spotter dots

[jthielen]

While the previous chase location app saved directly to placefiles, with #2 this info will instead be saved to a database. And so, we now need a placefile endpoint (in the fashion of the LSR placefile) for the chase teams to add to GR.

One extra point to keep in mind: for the replay (time-based) placefile, don't use all the locations in the history table. Instead, pick them out on a coarser time interval, such as the average radar scan interval.