add panning to pattern view

[nikhan]

since the x,y positions for blocks are screen dependent, it's very easy for someone with a large screen to move blocks into positions that are unavailable to those with smaller screens. (you can even make invisible blocks if too!)

panning would alleviate some of this problem. you could still pan like wild to -1000,-1000 and make your secret pattern there, but at least anyone would be able to access it.