Restricting "Add element" to the immediate fm-wrapper scope

This resolves a bug whereby two groups, named differently, with identically-named children, will have a conflict when blocks 2->n's "Add element" button is clicked. The second (or beyond) add element button adds an element in the correct place, based off the first wrapper's prototype.
Merge pull request #52 from mboynes/fixing-repeat-child-name-bug

Restricting "Add element" to the immediate fm-wrapper scope