Feature: Tooltip positioning/options

[jamietre]

Tooltip positioning can render on top of active area if the viewport boundaries do not permit correct positioning (nearest corner).

1 - detect viewport boundaries (right now only checks container boundaries) and attempt a different corner scheme if fails
2 - add callback on tooltip display allowing control over container position
3 - allow manual control of tooltip positioning (top/middle/bottom left/center/right, absolute, offsets) through an option

[jamietre]

1.2.4.055 improves tooltip positioning by not constraining it to the image dimensions. Still need to add end-user control over which corner or direct positioning.