Backend tests

moves tests from the wireclient-suite into a backend "behavior", which all three different implementations of `remoteStorage.remote` should expose / adhere to

todo: 

* [x] move more tests from the wireclient-suite into the backend behavior (only moved one so far, to try)
* [x] add the backend behavior as a test suite to the other two implementations
* [x] fix tests that test the wrong missing fileId behavior in GD
* [x] put stuff from the tests into helper functions
* [x] remove non-essential log statements