getElement(element) {
    element = this.options.container || element
    if (element instanceof jQuery) {
      element = element[0]
    } else if (typeof element === 'string') {
      element = document.querySelector(element)
    }
    return element
  }
parses `container` option or returns element
@param  {Object|string|HTMLElement} element
@return {HTMLElement} parsedElement