[Notice] In XOOPS Cube Legacy which can have many themes with different render- systems, that one render-system has the control to change themes is wrong, because this action can't list up themes of other render-systems. The action to change themes should be in Legacy. And, each render-systems should send theme informations through delegate-mechanism.
Therefore, this class is test for that we may move this action from LegacyRender module. If you want to check the concept of this strategy, see ThemeSelect preload in Legacy module.