[ahrs] float_dcm: fix comment
[dox] imu units
[dox] fix some units
[conf] Quad_LisaMX with F4 and mlkf
[nps] calc magnetic field at location
[nps] get rid of stupid warnings
[nps] add math/pprz_geodetic_wmm2010.c
[build] don't complain on build if dfu-util is not found
[nps] set gps week and tow

currently still hardcoded to May 2014, needs to be implemented properly
[messages] GPS_INT: pacc, sacc are unsigned

thanks Antoine
[ahrs] do not require AHRS_H_x if mag is not even used
[conf] update some example airframes