Update hierarchical tests to use dstore/Tree
createHierarchicalStore: Fix top-level filter

Use getRootCollection, but redefine it to work with our test data
Use dstore/Tree in more tests

* Fix IDs in rest.php and convert strings to use single quotes
* Use dstore/Tree in Rest.html
* Use dstore/Tree in Tree-expand-promise unit tests
createAsyncStore: Remove obsolete TODO
Add 0.4 migration guide
Make revisions to 0.4 migration guide, and add link to README
Migration guide: add information on hierarchical stores
0.4 Migration Guide: Refinements to hierarchical store section
Docs: Move util/mouse replacement notes into 0.4 Migration Guide

Remove util/mouse from doc TOC but leave a placeholder page pointing to the
0.4 Migration Guide
Documentation tweaks and updates

* Revise wordings
* Remove CHANGES.md and its mention in docs/README.md
* Remove "as of dgrid 0.3.x" and Dojo-1.7-specific comments
* Reduce wording in Tree docs to mention dstore/Tree
* Add notes about dgrid-autoheight to Styling page
* Update API comparison and include links to other doc pages
* Eliminate any remaining column plugin mentions