Set dummy menu vertical before updating camera to initial position

So that the update is actually effective in moving the camera to its
initial position

Note: The initial update must be called before
setStrictlyDownwards(true) so that the camera can adjust upwards
Backgrounds in LevelScreen are pixel perfect

Rather than adjusting to fit inside the viewportHeight/Width

Also added new extended background where the effects of this change can
be seen
Pixel perfect LevelChunk backgrounds and better code

viewportWidth/Height and screenWidth/Height are passed into the
constructor of a LevelChunk so that each individual method does not
require an argument for them