overlay.js: the submitterFn belongs to the SVGOverlay,
and so do some of the functions that had been assigned
to the SkeletonAnnotations. This includes the registering
of the SVGOverlay instance for use from so-called static
functions.

Additionally, refactored SVGOverlay to follow a style where each function
is declared independently of the others. Less indendation and clearer
reading of the object a function belongs to.