Customize the Trac workflow to allow us to "unassign" a ticket to return it to "new" status

[ryandesign (Ryan Carsten Schmidt)]

Currently, a ticket only has the "new" status when it is first created. If we assign a ticket to somebody, it then gets the "assigned" status. If later that person is no longer available to be a maintainer, we want to "unassign" the ticket and return it to "new" status, but the best we can do today is to "assign" it to the empty string, which can be confusing.

Trac has a ​customizable workflow. ​Here are some examples. I think we can probably get what we want with some small changes.