Let Range Facets Hang off of Pivots

Conceptually very similar to the previous sibling issues about hanging stats of pivots & ranges: using a "tag" on facet.range requests, we make it possible to hang a range off the nodes of Pivots.

Example...

facet.pivot={!range=r1}category,manufacturer
facet.range={tag=r1}price

...with the request above, in addition to computing range facets over the price field for the entire result set, the PivotFacet component will also include all of those ranges for every node of the tree it builds up when generating a pivot of the fields "category,manufacturer"

This should easily be combinable with the other sibling tasks to hang stats off ranges which hang off pivots. (see parent issue for example)