add autotrim feature to configuration tab

_locales/en/messages.json

@@ -611,6 +611,12 @@
     "featureFW_LAUNCH": {
         "message": "Permanently enable Launch Mode for Fixed Wing"
     },
+    "featureFW_AUTOTRIM": {
+        "message": "Continuously trim servos on Fixed Wing"
+    },
+    "featureFW_AUTOTRIMTip": {
+        "message": "When flying in a stabilzied mode, continuosusly adjust the servo midpoints so that the airplane keeps flying straight when switching to manual mode. Requires GPS."
+    },
     "featureDYNAMIC_FILTERS": {
         "message": "Dynamic Gyro Filters"
     },

js/fc.js

@@ -577,7 +577,8 @@ var FC = {
             {bit: 30, group: 'other', name: 'FW_LAUNCH', haveTip: false, showNameInTip: false},
             {bit: 2, group: 'other', name: 'TX_PROF_SEL', haveTip: false, showNameInTip: false},
             {bit: 0, group: 'other', name: 'THR_VBAT_COMP', haveTip: true, showNameInTip: true},
-            {bit: 3, group: 'other', name: 'BAT_PROFILE_AUTOSWITCH', haveTip: true, showNameInTip: true}
+            {bit: 3, group: 'other', name: 'BAT_PROFILE_AUTOSWITCH', haveTip: true, showNameInTip: true},
+            {bit: 31, group: 'other', name: "FW_AUTOTRIM", haveTip: true, showNameInTip: true}
         ];
 
         if (semver.gte(CONFIG.flightControllerVersion, "2.4.0") && semver.lt(CONFIG.flightControllerVersion, "2.5.0")) {