Implement export of item icons and locale

Add mod and command for exporting the Factorio locale including mods,
and item icons assemled into a sprite sheet including mods.

lua/export/info.json

@@ -0,0 +1,8 @@
+{
+    "name": "export",
+    "version": "0.0.0",
+    "title": "Icon exporter",
+    "author": "Clusterio Team",
+    "homepage": "https://github.com/clusterio/factorioClusterio",
+    "description": "Exports item prototypes on stdout during the data stage."
+}