Proper data manager restart handling

Introduce SYS_RESTART_TYPE parameter having one of 3 values: boot
restart, inflight restart, or unknown restart, and defaulting to unknown
restart.

px4io.cpp sets this parameter according to the type of restart detected.

dataman.c retrieves this parameter and clears data entries according to
their persistence level. Does nothing if unknown restart.
add options do disable or fake gps output in rcS
remove whitespace
Merge pull request #875 from PX4/gpsflag

rcS: add options to disable or fake gps output
Merge pull request #874 from jean-m-cyr/master

Proper data manager restart handling
mc_att_control: yaw feed-forward in manual control modes fixed
Merge pull request #880 from PX4/yaw_ff_fix

mc_att_control: yaw feed-forward in manual control modes fixed
Merge branch 'master' of github.com:PX4/Firmware into ekf_params