Update documentation from dojo/store to dstore

* Update 'store' property references to 'collection'
* Update dojo/store references to dstore
* Update references to store APIs
* Remove a couple of stale references to column plugins
Additional refinements to dstore-related docs
Additional 0.4 doc cleanup

* Remove remaining column plugin references
* Update usage comparison to use 1.8-supported parser features
Update dijit_layout.html test page for Dojo 1.8+