AP_NavEKF2: Use SI units conventions in parameter units

Follow the rules from:
http://physics.nist.gov/cuu/Units/units.html
http://physics.nist.gov/cuu/Units/outside.html
and
http://physics.nist.gov/cuu/Units/checklist.html
one further constrain is that only printable (7bit) ASCII characters are allowed

libraries/AP_NavEKF2/AP_NavEKF2.cpp

@@ -192,7 +192,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Range: 0 250
     // @Increment: 10
     // @User: Advanced
-    // @Units: milliseconds
+    // @Units: ms
     AP_GROUPINFO("GPS_DELAY", 8, NavEKF2, _gpsDelay_ms, 220),
 
     // Height measurement parameters
@@ -227,7 +227,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Range: 0 250
     // @Increment: 10
     // @User: Advanced
-    // @Units: milliseconds
+    // @Units: ms
     AP_GROUPINFO("HGT_DELAY", 12, NavEKF2, _hgtDelay_ms, 60),
 
     // Magnetometer measurement parameters
@@ -238,7 +238,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Range: 0.01 0.5
     // @Increment: 0.01
     // @User: Advanced
-    // @Units: gauss
+    // @Units: Gauss
     AP_GROUPINFO("MAG_M_NSE", 13, NavEKF2, _magNoise, MAG_M_NSE_DEFAULT),
 
     // @Param: MAG_CAL
@@ -328,7 +328,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Range: 0 127
     // @Increment: 10
     // @User: Advanced
-    // @Units: milliseconds
+    // @Units: ms
     AP_GROUPINFO("FLOW_DELAY", 23, NavEKF2, _flowDelay_ms, FLOW_MEAS_DELAY),
 
     // State and Covariance Predition Parameters
@@ -364,7 +364,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Description: This noise controls the rate of gyro scale factor learning. Increasing it makes rate gyro scale factor estimation faster and noisier.
     // @Range: 0.000001 0.001
     // @User: Advanced
-    // @Units: 1/s
+    // @Units: Hz
     AP_GROUPINFO("GSCL_P_NSE", 27, NavEKF2, _gyroScaleProcessNoise, GSCALE_P_NSE_DEFAULT),
 
     // @Param: ABIAS_P_NSE
@@ -464,7 +464,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Description: This state process noise controls the growth of earth magnetic field state error estimates. Increasing it makes earth magnetic field estimation faster and noisier.
     // @Range: 0.00001 0.01
     // @User: Advanced
-    // @Units: gauss/s
+    // @Units: Gauss/s
     AP_GROUPINFO("MAGE_P_NSE", 40, NavEKF2, _magEarthProcessNoise, MAGE_P_NSE_DEFAULT),
 
     // @Param: MAGB_P_NSE
@@ -472,7 +472,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Description: This state process noise controls the growth of body magnetic field state error estimates. Increasing it makes magnetometer bias error estimation faster and noisier.
     // @Range: 0.00001 0.01
     // @User: Advanced
-    // @Units: gauss/s
+    // @Units: Gauss/s
     AP_GROUPINFO("MAGB_P_NSE", 41, NavEKF2, _magBodyProcessNoise, MAGB_P_NSE_DEFAULT),
 
     // @Param: RNG_USE_HGT
@@ -515,7 +515,7 @@ const AP_Param::GroupInfo NavEKF2::var_info[] = {
     // @Range: 0 127
     // @Increment: 10
     // @User: Advanced
-    // @Units: milliseconds
+    // @Units: ms
     AP_GROUPINFO("BCN_DELAY", 46, NavEKF2, _rngBcnDelay_ms, 50),
 
     // @Param: RNG_USE_SPD