OP-1412 change initial gyro bias uncertainty variance setting

from 1e-4 to 1e-6 to allow more stable filter initialization.
this is now valid thanks to available temp compensation and gyro bias
calibration in GCS
OP-1412 delay ekf initialization until magnetometers are reporting valid data
OP-1412 change systemalarms to update periodic to not loose data
OP-1412 do not dicard mags after init
Merge branch 'corvuscorax/OP-1412_Gyrodrift_issue' into rel-14.06