Map Fixes / Enhancements

I finally did some work on the map page. The map now displays stations which report status in the most recent hour but haven't heard anything or been heard. It will show their Tx percentage, frequency, and dBm (this information is reported by WSPR 1.0 in place of a spot upload each time slot in which nothing is decoded). So now we can have an idea of the activity on a band when propagation is poor.

Also, stations which report themselves as receive-only are flagged in red rather than blue.

Finally, I fixed a longstanding bug in the heard and heardby lists: if the heard- or heard-by list was empty, it would sometimes show another stations' list.