Fixing bug where SyncProjectsAndEnvironments failed on undefined method

This was caused by DNEnvironmentList, however
DNProject::DNEnvironmentList() returning the wrong container. It used
filterByCallback which returns an ArrayList.

The whole thing of overloaded the static get() on DNEnvironment and
DNProject seemed hacky, so I've removed that and refactored the sync
and remove obsolete methods onto SyncProjectsAndEnvironments. It seems
like they belong here anyway, not on the lists themselves.