rest.php: Fix total/end-of-range inconsistency issues
Add initial implementation of client-side JsonRest mock service

This mock service requires specific loader configuration to essentially
hijack dojo/_base/xhr, since it is impossible to implement mock services
for JsonRest using xhrPlugins (which only affects dojo.xhr* calls, not calls
to xhr directly).  dojo/request/registry is also not an option since
dojo/_base/xhr references dojo/request/xhr directly, and dojo/request isn't
available in Dojo 1.7 regardless (which dgrid still supports).

Also removed test/data/rest.js which has been unused for a while.
test/data/restXhr: Refactor logic to generate query results dynamically

This allows for nested child levels without a huge hit on performance,
as opposed to pre-generating all items in-memory.

Also fixed a few straggling pieces from back when this was targeting the
existing "rest.php?" URL.
test/data/restXhr: Add more comments, use mixin for reset args
Convert other test pages to use test/data/restXhr