Merging and remapping of IVStores and InternalLists

Add merge() methods to IndexValueStore and InternalList, which merge
another store/list in to the current one and return a mapping
translating old indexes to new ones.

Also add functions that, given such a mapping, traverse a linear
model data array and remap store/list indexes using simple logic for
annotations and node type-specific functions for node attributes.

Change-Id: I1e90755ced1a87c190947c037cf151c4d17cf8b7
Merge "Merging and remapping of IVStores and InternalLists"