Update dstore range API use in Tree and Pagination
OnDemand_promises test: Add RequestMemory store

FIXME: RequestMemory seems to only report first page size as total
DnD: Update to use dstore's beforeId option
Pagination: Update code to no longer reference collection.data
_StoreMixin: renderCollection -> renderQueryResults

This accounts for recent changes to dstore, after which we can expect a
QueryResults object to be passed to this method at all times with one
minor change to dgrid/Tree.
_StoreMixin: Don't forget to update this.collection in _setCollection

This actually prevents an unexpected error in Pagination when collection is
set to null
Update errorStores based on latest dstore changes
ODL: Reference totalLength, not total