Adding new follow target navigation and main states. New follow target

topic added. New follow fsm added to the navigator

msg/follow_target.msg

@@ -0,0 +1,11 @@
+uint64 timestamp		# timestamp, UNIX epoch (GPS synced)
+uint8 est_capabilities		# Flags to indicate which quantities the tracker knows about: (POS, VEL, ACCEL, ATT + RATES)
+uint32 lat			# target position (deg * 1e7)
+uint32 lon			# target position (deg * 1e7) 
+float32 alt			# target position 
+float32[3] velocity		# target velocity (AMSL, meters) # target position (0 0 0 for unknown)
+float32[3] accel		# target acceleration (linear) in earth frame. 
+float32[4] attitude_q		# where the target is facing. 
+float32[3] rates		# (0 0 0 for unknown)
+float32[3] pos_cov		# uncertainly in earth frame for X, Y and Z. We will need to agree on the exact format here -1 for unknown
+uint64 custom_state		# A custom vector, can be used to transmit e.g. button states or switches of a tracker device

msg/vehicle_status.msg

@@ -11,7 +11,8 @@ uint8 MAIN_STATE_STAB = 8
 uint8 MAIN_STATE_RATTITUDE = 9
 uint8 MAIN_STATE_AUTO_TAKEOFF = 10
 uint8 MAIN_STATE_AUTO_LAND = 11
-uint8 MAIN_STATE_MAX = 12
+uint8 MAIN_STATE_AUTO_FOLLOW_TARGET = 12
+uint8 MAIN_STATE_MAX = 13
 
 # If you change the order, add or remove arming_state_t states make sure to update the arrays
 # in state_machine_helper.cpp as well.
@@ -47,7 +48,8 @@ uint8 NAVIGATION_STATE_STAB = 15		# Stabilized mode
 uint8 NAVIGATION_STATE_RATTITUDE = 16		# Rattitude (aka "flip") mode
 uint8 NAVIGATION_STATE_AUTO_TAKEOFF = 17	# Takeoff
 uint8 NAVIGATION_STATE_AUTO_LAND = 18		# Land
-uint8 NAVIGATION_STATE_MAX = 19
+uint8 NAVIGATION_STATE_AUTO_FOLLOW_TARGET = 19	# Auto Follow
+uint8 NAVIGATION_STATE_MAX = 20
 
 # VEHICLE_MODE_FLAG, same as MAV_MODE_FLAG of MAVLink 1.0 protocol
 uint8 VEHICLE_MODE_FLAG_SAFETY_ARMED = 128