The objective is to add a $depth attribute so that it is possible to reach up to retrieve the parameters of ancestor transclusions. However, doing so requires changing the encoding of parameter names so that it is not possible for a user parameter to clash with an attribute like $depth. So now we have to double up dollars on any attribute names seen by the parameters widget, just like with the transclude widget itself.
There are two big changes here:
Replace the previous "ts-wrapper" mechanism, which we had been using to redefine custom widgets inside their definitions to prevent recursive calls. Now we've got the genesis widget we can instead control recursion through a new "$remappable" attribute that allows the custom widget mechanism to be skipped.
We also extend the slot widget to allow a depth to be specified; it then reaches up by the indicated number of transclusion widgets to find the one from which it should retrieve the slot value.
