[conf] ins_float_invariant: simpler AHRS_*_FREQUENCY defaults
fix typos in CHANGELOG
[airborne] some minor style fixes
[fixedwing] rename LOW_BATTERY_KILL_DELAY to CATASTROPHIC_BAT_KILL_DELAY
[tmtc] gpsd2ivy: commandline options and verbose mode

- fix nan checks and warnings
- default to broadcast instead of multicast on linux
- make ivy_bus, gpsd server and port configurable via commandline
- added verbose mode which should help to track down issue #658
[gps] Add a new GPS based on the datalink
[ground_segment] Add Optitrack to Ivy service
[gps] GPS datalink update to newest master.
[ins] Added the possibility to use GPS for altitude estimation
[optitrack] INS and AHRS improvements
[fms_network] Added multicast and updated optitrack speed differentation
[ardrone] Updated gains for inside
[optitrack] Renamed to NatNet and added more options
[gps] Added doxygen documentation to the GPS datalink subsystem