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/control.lua

@@ -0,0 +1,8 @@
+local function send_json(channel, data)
+    data = game.table_to_json(data)
+    print("\f$ipc:" .. channel .. "?j" .. data)
+end
+
+script.on_init(function()
+    send_json("mod_list", game.active_mods)
+end)