Filter out junk data

[mattrasband]

Before GPS lock, garbage data may be sent to the server as gps coordinates. We need to filter incoming data in a logical manner to not render bad points on the map.

Possible solutions include:

1. Ignoring anything outside the U.S. (makes us less portable)
2. buffering a few points and trashing any that don't fall in a logical path (I.e. A balloon would not jump from 0,0 to 39,-104 between points)