constructor(externalPlugins = [], playerId = 0) {
      this.playerId = playerId

      this.playbackPlugins = [...registry.playbacks]

      const { core, container } = Loader.registeredPlugins
      this.containerPlugins = Object.values(container)
      this.corePlugins = Object.values(core)

      if (!Array.isArray(externalPlugins))
        this.validateExternalPluginsType(externalPlugins)

      this.addExternalPlugins(externalPlugins)
    }
builds the loader
@method constructor
@param {Object} externalPlugins the external plugins
@param {Number} playerId you can embed multiple instances of clappr, therefore this is the unique id of each one.