ImportSongs: Add plugin support

- Files with filenames that end with .taikoweb.js can be imported and run to add custom functionality to the game
- The plugin file is a javascript module script that should have a class in the default export
- Currently supported methods in the class: name (string), load, start, stop, unload (functions)
- The class can be extended from the Patch class to add automatic patching of variables and functions
- Here are some of the plugins I made: https://github.com/KatieFrogs/taiko-web-plugins

public/src/js/loader.js

@@ -1,5 +1,8 @@
 class Loader{
-	constructor(callback){
+	constructor(...args){
+		this.init(...args)
+	}
+	init(callback){
 		this.callback = callback
 		this.loadedAssets = 0
 		this.assetsDiv = document.getElementById("assets")
@@ -253,6 +256,7 @@ class Loader{
 			pageEvents.setKbd()
 			scoreStorage = new ScoreStorage()
 			db = new IDB("taiko", "store")
+			plugins = new Plugins()
 			
 			Promise.all(this.promises).then(() => {
 				if(this.error){