Analyst not required but if missing analysis cannot be transitioned

[mikejmets]

Steps to reproduce

Create a AR
Add a result value for an analyses and do NOT select an analyst

Current behavior

That analysis will not be transitioned and cannot be transition thereafter.

Expected behavior

Either the analyst field must be mandatory or the user has a way to add the analyst after submission

[mikejmets]

For BC I decided to make analyst mandatory and added the following code to browser/analysisrequest/workflow.py

            if uid in analysts and analysis_active:
                if len(analysts[uid]) == 0:
                    title = safe_unicode(analysis.getService().Title())
                    msgid = _('Analyst for ${analysis} is required.',
                              mapping={'analysis': title})
                    message = safe_unicode(t(msgid))
                    self.context.plone_utils.addPortalMessage(message, 'error')
                    continue
                analysis.setAnalyst(analysts[uid])