CreateOrCommentHandler should have parameter for priority

Creating an issue via email works great for us.

Due to some persons use of emails (sending them with high priority regardless of content) they always end up in jira as blocker. Because of the political implications of "downprioritizing" an issue, we usually don't do this, but it really screws up our statistics. I'd rather prioritize some initially "normal" support request up to blocker, thus I'd like the CreateOrCommentHandler to offer a parameter for the standard priority. It could and should still default to the current behaviour, if this parameter is not given.