msg: update estimator_status

Reduce unnecessary length of state and covariance arrays
Add time slip monitor

msg/estimator_status.msg

-float32[32] states		# Internal filter states
+float32[24] states		# Internal filter states
 float32 n_states		# Number of states effectively used
 float32[3] vibe			# IMU vibration metrics in the following array locations
 # 0 : Gyro delta angle coning metric = filtered length of (delta_angle x prev_delta_angle)
@@ -7,7 +7,7 @@ float32[3] vibe			# IMU vibration metrics in the following array locations
 uint8 nan_flags			# Bitmask to indicate NaN states
 uint8 health_flags		# Bitmask to indicate sensor health states (vel, pos, hgt)
 uint8 timeout_flags		# Bitmask to indicate timeout flags (vel, pos, hgt)
-float32[28] covariances	# Diagonal Elements of Covariance Matrix
+float32[24] covariances	# Diagonal Elements of Covariance Matrix
 uint16 gps_check_fail_flags     # Bitmask to indicate status of GPS checks - see definition below
 # bits are true when corresponding test has failed
 uint16 GPS_CHECK_FAIL_MIN_SAT_COUNT = 0			# 0 : minimum required sat count fail
@@ -84,4 +84,4 @@ uint16 solution_status_flags # Bitmask indicating which filter kinematic state o
 # 8 - True if the EKF has sufficient data to enter a mode that will provide a (relative) position estimate
 # 9 - True if the EKF has sufficient data to enter a mode that will provide a (absolute) position estimate
 # 10 - True if the EKF has detected a GPS glitch
-
+float32 time_slip # cumulative amount of time in seconds that the EKF inertial calculation has slipped relative to system time