test for 'r' or no access on write/read

even in anonymous mode, the app should have claimed 'r' or 'rw' access to the module it's accessing. otherwise you'll get 401s later and it'll be more messy. we could at least warn about this with a warning, as appropriate:

* WARNING: please call `remoteStorage.acces.claim('foo', 'r')` (read only) or  `remoteStorage.acces.claim('foo', 'rw')` (read/write) first
* WARNING: editing a document to which only read access ('r') was claimed
I think it would be better to use the actual path in the warning message instead of 'foo'.