Imu2d static initialization

Finished the gtests for the static initialization, they pass.

include/imu/factor/factor_imu.h

@@ -4,6 +4,7 @@
 //Wolf includes
 #include "imu/feature/feature_imu.h"
 #include "imu/sensor/sensor_imu.h"
+#include "imu/processor/processor_imu.h"
 #include "core/factor/factor_autodiff.h"
 #include "core/math/rotations.h"