There seems to be a bug in the backend, but I have no idea what's wrong.
Clearing the start screen with a ClearRect call renders the 2D drawer in an unstable state. So for now, clear the screen by rendering a texture, but with light color black, which produces the same effect without later breaking stuff.
* for Strife the game palette must be loaded before the start screen.
* increase update frequency of start screen to roughly 35 fps
* fixed Strife's laser sprite names.
* do not show the native progress bar if a graphical start screen is used.
