Added in a spot for drawArrow() in the map maker, which needs to be finished out.

Basically Wilbur can find what he feels is a suitable JS function, or I will search the internet for the buggiest, worst written hack and implement it with gratuitous printf() statements.

Either way, we need an arrow drawn from the middle front edge to the middle back edge of a cabinet to indicate air flow.  Black, as the arrow shouldn't change based upon stats,

#318
Merge branch 'master' of https://github.com/samilliken/openDCIM