The PluginManager calls this method on a Global Plugin when the plugin is first instantiated.
It will never be called again on this instance.
In here you can set-up whatever you need for this plugin to run.
If a plugin is set to automatically start then
BasePlugin.start will be called immediately after this.
On a Scene Plugin, this method is never called. Use Phaser.Plugins.ScenePlugin#boot instead.
A value specified by the user, if any, from the