Edit WebSubmit Function

A referee may either "accept" or "reject" a refereed document.
The referee's decision is stored in a file in the submission's working
directory and it is this function's job to read the contents of that
file and update the status of the document's entry in the approvals
table (sbmAPPROVAL) to be either "accepted" or "rejected" depending
upon the referee's decision.

@param decision_file: (string) - the name of the file in which the
    referee's decision is to be found.
    NOTE: A referee's decision _MUST_ be either "accept" or "reject".
          If not, an InvenioWebSubmitFunctionError will be raised.
          If a document's "approval status" is not "waiting" at the
          time of the referee's decision, the decision will not be
          taken into account and the submission will be halted.
          (This is because it's not appropriate to approve a document
          that has already been approved or rejected, has been
          withdrawn, etc.)

@return: empty string.

@Exceptions raised: InvenioWebSubmitFunctionError on unexpected error.
                    InvenioWebSubmitFunctionStop in the case where the
                    approval should be stopped for whatever reason.
                    (E.g. when it has already been approved.)