Formerly the mouse texture was only used when the overlay was visible. When
only the game screen was visible, the code rendered the mouse cursor on the
game screen texture.
This simplifies the drawing pipeline a bit.
This is used to provide default implementations for createConfigWriteStream
and createConfigReadStream, which can be used by most backends.
Note that backends can still override createConfigRead/WriteStream;
this could be useful if settings on some port are not stored in a
regular file (think 'Windows registry', for a hypothetical example).
We now delay the mouseup events for 50ms, rather than just delaying them for an additional couple of pollEvent (which doesn't work anymore due to changes in the eventhandling code elsewhere). This fixes#3018512.
