Compact Overlay: auto aspect ratio, remember size, auto switch (Issue #278)

Implemented these features (Issue #278):

• Open the compact overlay window with the correct aspect ratio
• Save the size of the compact overlay window, so I don’t have to resize it every time I switch
• Auto toggle to compact overlay when the app window loses focus, so I can switch to another app while I still watching a video very fast

Also, fixed issue #255