static getRegistered(type = false) {
    const types = Object.keys(control.classRegister)
    if (!types.length) {
      return types
    }
    return types.filter(key => {
      // if type is specified, then we want to return all subtypes
      // of that type (registered with the key <type>.<subtype>)
      if (type) {
        return key.indexOf(type + '.') > -1
      }
      return key.indexOf('.') === -1
    })
  }
Looks up the classRegister & returns registered types or subtypes
@param  {string|false} type optional type of control we want to look up
subtypes of. If not specified will return all types
@return {Array} registered types (or subtypes)