feat(plugin): Add JS Plugin class file

Plugin dev from the  JS based project could face extra work
because of the TS based Plugin class.
So, providing JS version will solve the issue.

Fix #1665

src/Plugin/Plugin.js

@@ -0,0 +1,74 @@
+/**
+ * Copyright (c) 2017 ~ present NAVER Corp.
+ * billboard.js project is licensed under the MIT license
+ */
+/**
+ * Base class to generate billboard.js plugin
+ * @class Plugin
+ */
+/**
+ * Version info string for plugin
+ * @name version
+ * @static
+ * @memberof Plugin
+ * @type {string}
+ * @example
+ *   bb.plugin.stanford.version;  // ex) 1.9.0
+ */
+export default class Plugin {
+	/**
+	 * Version info string for plugin
+	 * @name version
+	 * @static
+	 * @memberof Plugin
+	 * @type {String}
+	 * @example
+	 *   bb.plugin.stanford.version;  // ex) 1.9.0
+	 */
+	static version = "#__VERSION__#";
+
+	/**
+	 * Constructor
+	 * @param {Any} options config option object
+	 * @private
+	 */
+	constructor(options = {}) {
+		this.$$;
+		this.options = options;
+	}
+
+	/**
+	 * Lifecycle hook for 'beforeInit' phase.
+	 * @private
+	 */
+	$beforeInit() {}
+
+	/**
+	 * Lifecycle hook for 'init' phase.
+	 * @private
+	 */
+	$init() {}
+
+	/**
+	 * Lifecycle hook for 'afterInit' phase.
+	 * @private
+	 */
+	$afterInit() {}
+
+	/**
+	 * Lifecycle hook for 'redraw' phase.
+	 * @private
+	 */
+	$redraw() {}
+
+	/**
+	 * Lifecycle hook for 'willDestroy' phase.
+	 * @private
+	 */
+	$willDestroy() {
+		Object.keys(this).forEach(key => {
+			this[key] = null;
+			delete this[key];
+		});
+	}
+}