Improve error message returned when attempting to update an issue in a non editable workflow state

It is possible to configure a Jira workflow such that an issue can't be edited based on a particular status. When attempting to update the issue using the REST API, Jira returns a message like “Field ‘customfield_13902’ cannot be set. It is not on the appropriate screen, or unknown.” This error is somewhat confusing the app developers. An improved error would be something like “Issue XXX in state YYY is not editable due to workflow settings”.