prepare localstorage to support user metadata

In stat() take metadata from the function stub
get_user_metadata() instead of leaving it empty
adjust unittests.py to 4 space indent
adapt the unittests to use the sqlalchemy backend
let the register_data_object() function return true

the result value is not used anywhere, so jsut return something
simple.
this is interesting to build an appropriate mock object
in the unittests