FCCdata: Tower payload

Implemented the Tower Payload option for public use. Previously, this was an REC internal function. Tower Payload allows users to see which other FM and TV facilities use the same coordinates. This function can be used to identify facilities in order to calculate RF radiation on a particular tower, especially in light of the recent increased awareness in ET Dockets 03-137 and 13-84. The Tower Payload function can be found in the sidebox on FM engineering records. This function works similar to how the "What's On This Tower" function on the FCCdata mobile presentation works.