autotest: added developer build support

this creates firmware builds for developers in the devbuild directory
autotest: added link to devbuild tree
AP_HAL_Linux: [Bugfix] prevent memory acces violation in process_dsm_pulse

When a S.Bus signal is fed into the rcin-Pin AruPlane on the BBB get's a
Segmentation fault. This patch prevents the memory acces to dsm_state.bytes[16] outside
of the array bounds. The patch should be reviewed by sombody who knows the DSM protocol,
as i don't.
scripts: fixed devrelease permissions
DataFlash: add UBX3 message for accuracy logging
AP_GPS: Add uBlox accuracy metrics interface and logging