Fix bugs

Bug1：
Every time we change scene，it seems that the SVPProgress will add two
window objects but just remove one. So after changing, the windows
array is always incresing.
Solution: I don't know where it add windows so that I just remove all
windows except the first one.
Bug2:
After change scene, the text field can't be edited because the key
window is wrong.
Solution: Because the bug1 is soloved, there is only one window now.
Every clear residual winows, I set the key window and set it visible.