installer:fixed the Font out of the boxmessage in slideshow

And hide the shadow of boxmessage

tower:https://tower.im/projects/8f19f0bf0e754f0b82ef2c24bc230973/todos/5d62d00bfc754c03a6ab75ef9d7d661a/
Change-Id: Ie8a833ed90a02a572c7f84b2046c40d9bf83d007