Added controller to retrieve child page list over AJAX
Added controller to retrieve child page list over AJAX

- Broke child page list plugin into two controllers (one to handle processing URL options, caching and templating, and one to do the querying)
- Updated init.php plugin registration to register first controller as the controller for child page list plugin.
- Controller which just handles querying can be accessed via AJAX to get a json encoded array of pages.

boomcms/boom-core,boomcms/boom-core,boomcms/boom-core