workflows: fix for Celery worker tasks loading

* Loads the Celery worker tasks so that Invenio Celery wrapper
  can discover the tasks.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
jsonalchemy: create_record error catching

* The marc reader and wrapper modules now catches any errors
  while parsing MARCXML with legacy create_record and returns a
  ReaderException with details.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>
records: API test case addition

* In response to 5daee2f, adds a new test-case to make sure
  an exception is raised when Record.create is called with bad
  data.

Signed-off-by: Jan Aage Lavik <jan.age.lavik@cern.ch>