Refactor world bootstrap and allow empty startup worlds

shared/data/ship-types.json

@@ -0,0 +1,24 @@
+[
+  "resupplier",
+  "miner",
+  "carrier",
+  "fighter",
+  "heavyfighter",
+  "destroyer",
+  "largeminer",
+  "freighter",
+  "bomber",
+  "scavenger",
+  "frigate",
+  "transporter",
+  "interceptor",
+  "scout",
+  "courier",
+  "builder",
+  "corvette",
+  "police",
+  "battleship",
+  "gunboat",
+  "tug",
+  "compactor"
+]