Backport Flightgear server from private tx branch, collapse commits.

* Added Flightgear multiplayer output interface to uhd_modes.py. This allows flight with live traffic in fgfs.
* Quaternion library borrowed from PyPi and modified to generate angle/axis representation and construct rotation quat from lat/lon to ECEF.
* Miscellaneous enhancements and cleanup to fix timestamps, add aircraft type field (seems to be unused anyway), turnrate info

python/__init__.py

@@ -56,6 +56,8 @@ from modes_sql import modes_output_sql
 from modes_sbs1 import modes_output_sbs1
 from modes_kml import modes_kml
 from modes_raw_server import modes_raw_server
+from modes_flightgear import modes_flightgear
+from Quaternion import *
 
 # ----------------------------------------------------------------
 # Tail of workaround