Simplify the Contacts module code...

... but just move the complexity to the application code, to deal with
'undefined'. I'm waiting for an answer if it's behaving like specified.

This is related to remotestorage/remotestorage.js#597 and
remotestorage/modules#26
Merge pull request #5 from gregkare/simplify_contacts_module

Simplify the Contacts module code...