Implement autosaving of data held in memory

Add controller.autosave_interval config that specifies the frequency
which controller config, hosts, instances, users, mod packs and plugin
specific data which is held in memory should be automatically flushed to
disk if they have changed since the last time they were saved.  This
prevents data loss in the event of a server crash.

Plugins can use the onSaveData hook to save its own data at the same
time as the controller does and this obsoletes making an autosave
interval in the plugin.

Resolves #523.

packages/controller/src/UserManager.ts

@@ -10,6 +10,7 @@ import * as lib from "@clusterio/lib";
 export default class UserManager {
 	roles: Map<number, lib.Role> = new Map();
 	users: Map<string, lib.User> = new Map();
+	dirty = false;
 
 	constructor(
 		private _config: lib.ControllerConfig
@@ -41,10 +42,6 @@ export default class UserManager {
 	}
 
 	async save(filePath:string): Promise<void> {
-		if (this.roles.size === 0 || this.users.size === 0) {
-			return;
-		}
-
 		let serializedRoles = [];
 		for (let role of this.roles.values()) {
 			serializedRoles.push(role.serialize());
@@ -59,6 +56,7 @@ export default class UserManager {
 			users: serializedUsers,
 			roles: serializedRoles,
 		};
+		this.dirty = false;
 		await lib.safeOutputFile(filePath, JSON.stringify(serialized, null, "\t"));
 	}
 
@@ -80,6 +78,7 @@ export default class UserManager {
 
 		let user = new lib.User({ name, roles }, this.roles);
 		this.users.set(name, user);
+		this.dirty = true;
 		return user;
 	}