Fix this is not a constructor error on startup

When passing methods around they lose their binding to this, which means
the fromJSON methods no longer has this be their class.  Fix by binding
the methods to the class they belong to before passing them on to the
datastore.

packages/controller/src/Controller.ts

@@ -102,12 +102,12 @@ export default class Controller {
 
 		const systems = new lib.SubscribableDatastore(...await new lib.JsonIdDatastoreProvider(
 			path.join(databaseDirectory, "systems.json"),
-			lib.SystemInfo.fromJSON
+			lib.SystemInfo.fromJSON.bind(lib.SystemInfo)
 		).bootstrap());
 
 		const hosts = new lib.SubscribableDatastore(...await new lib.JsonIdDatastoreProvider(
 			path.join(databaseDirectory, "hosts.json"),
-			HostInfo.fromJSON,
+			HostInfo.fromJSON.bind(HostInfo),
 			this.migrateHosts, this.finaliseHosts,
 		).bootstrap());
 
@@ -119,12 +119,12 @@ export default class Controller {
 
 		const saves = new lib.SubscribableDatastore(...await new lib.JsonIdDatastoreProvider(
 			path.join(databaseDirectory, "saves.json"),
-			lib.SaveDetails.fromJSON
+			lib.SaveDetails.fromJSON.bind(lib.SaveDetails)
 		).bootstrap());
 
 		const modPacks = new lib.SubscribableDatastore(...await new lib.JsonIdDatastoreProvider(
 			path.join(databaseDirectory, "mod-packs.json"),
-			lib.ModPack.fromJSON
+			lib.ModPack.fromJSON.bind(lib.ModPack)
 		).bootstrap());
 
 		const userManager = new UserManager(config);