Add reserve fuel tank capacities to ships

These contribute towards ship mass, and are necessary for accurate jump
range calculation.

Ref: https://forums.frontier.co.uk/threads/reserve-tank-sizes-for-all-ships.460434/

ships/imperial_courier.json

@@ -20,7 +20,8 @@
       "pitch": 38,
       "roll": 90,
       "yaw": 16,
-      "crew": 1
+      "crew": 1,
+      "reserveFuelCapacity": 0.41
     },
     "retailCost": 2542930,
     "requirements": {