Create initial message schemas

Closes #7 (closed)

examples/ecosub_c2/mission_plan.json

   "delivery_type": "publish",
   "encoded": false,
   "message_type": "mission_plan",
-  "platform_serial": "reav-60",
+  "platform_ID": 1,
   "autonomy_engine_mission_plan_ID": 1,
   "plan": [
     {

examples/ecosub_c2/platform_status.json

     "longitude": -10.122,
     "depth": 50,
     "altitude": 20,
+    "heading": 90.0,
     "health_status": "Warning",
     "localisation_error": null,
     "usbl_fix_seconds_ago": null,

examples/hydrosurv_adapter/mission_plan.json

   "delivery_type": "publish",
   "encoded": false,
   "message_type": "mission_plan",
-  "platform_serial": "reav-60",
+  "platform_ID": 5,
   "autonomy_engine_plan_ID": 1,
   "plan": [
       {

examples/hydrosurv_adapter/platform_status.json

   "active": true,
   "status_source": "onboard_platform",
   "battery_remaining_capacity": 80.2,
+  "heading": 310.0,
   "health_status": "Lost Connection",
   "latitude": 178.2,
   "longitude": -10.122,