Refactor sync requests to use the collection handler to obtain changes.
Revert some code from a previous attempt at improving change detection.
Refactor GETITEMESTIMATE requests to use the collection handler.
Revert "Use callByPackage()."

This reverts commit 7efe54beb27ebfdd43fde22a0db3cf3f5b17dc24.

Can't do it this way, as 'links' is not considered when looking for
supported api methods of an application.