After enabling or disabling components, the Angular content may have
changed, so we must call CRM_Core_Resources::singleton()->resetCacheCode.
This commit does so in a few pieces:

 * It updates the admin UI so that it uses the API for saving changes to
   "enable_components". (This resolves a split where UI+API were different.)
 * It updates the "enable_components" setting so that changes trigger
   a cache-code reset.
 * It updates the settings framework so that callbacks can reference
   non-static functions. (The objects must be registered in "Container".)
 * It exposes some of our singletons (eg CRM_Core_Resources) as objects
   in "Container".
 * It adds a helper function (Civi\Core\Resolver) which can be used to
   convert references from data files (*.setting.php, *.xml, *.yml, etc)
   into objects/callables.
 * It updates various places that use callbacks from data files to
   go through Resolver.

See also: http://forum.civicrm.org/index.php/topic,35579.0.html