Some global offset system to support negative coords and other gimmicks

[LittleEndu]

• keep track of what was canvas' top-leftmost pixel coord when the template was uploaded
• guess or allow the user to specify what it actually is right now so that all the templates can be shifted
• in case of where top-leftmost isn't 0,0 (aka negative coords or shrinking canvas), allow templates to choose between UI coords or html canvas coords

this would hopefully make it less confusing to handle various expansion, contraction, 0/0 not being top-left, and other such gimmicks