Flip ordering of ribbon and jack updating

This fixes a bug where the ribbons would scroll if holding down a
direction that'd cause Jack to keep walking into a wall without actually
moving
Make actors respond to notifications from the world they are observing
Get rid of GetPrefix and have levels check for gaps again

Levels in this game should not have gaps in the tiles, so fix that.

Also, getPrefix is a function of the image loading, and since we're
properly using ImageLoader with the BricksManager the method is no
longer necessary