px4io: split io_handle_battery() out from io_handle_status()

ready to add vservo and rssi
uORB: added new servorail_status object

used for VSERVO and RSSI on FMUv2
px4io: added monitoring of vservo and vrssi

publish via servorail_status ORB topic
added error_count field to sensor report structures
perf: added perf_event_count() method

this allows drivers to get an event_count from a perf counter
Merge branch 'master' of github.com:PX4/Firmware into status_monitoring
drivers: report error_count in drivers where possible
Merge branch 'master' of github.com:PX4/Firmware into status_monitoring
Enabling navigator, does not do anything useful yet
Fix the direction of the override switch for the new state machine
RC3 usually used as Throttle, but trim was set to 1500 by default.
It should be 1000 by default.
There were unintialized variables.
(control mode was not updated)

Also, new flags (xy_valid etc) were considered.
Airframe No. 21. 22 have been added.
That is for general ESC with PX4IO (frame geometry defined)
easystar startup script: load mixer from sd-card if available
Merge pull request #427 from thomasgubler/sd_mixer

easystar startup script: load mixer from sd-card if available
Hotfix: Improved file test
Merge branch 'master' of github.com:PX4/Firmware
tone_alarm: add GPS warning tone
Better voltage scaling for Iris
Start digital airspeed sensors as default