function onSubmit(vRequest) {
			if (Array.isArray(vRequest)) {
				vRequest.forEach(onSubmit);
			} else if (vRequest.$submit) {
				vRequest.$submit();
			}
		}
Sends an OData batch request containing all requests referenced by the given group ID and
processes the responses by dispatching them to the appropriate handlers.

@param {string} sGroupId
  ID of the group which should be sent as an OData batch request
@returns {Promise}
  A promise on the outcome of the HTTP request resolving with <code>undefined</code>; it is
  rejected with an error if the batch request itself fails
@throws {Error}
  If there is already a batch request containing change requests

@private