Use done() to assert that last the 'then' executed

in a tag test
Add _test suffix to tags test file
Add Ticket#removeTag(...)
Add list of tags to ticket api instead of status string
Add 'nohandlers' tag to new tickets

and remove it automatically when a handler is added
Simplify ticket updates test

was way too fragile
Add models.client.Base#collection() shortcut
Loads tags for single ticket api too
Use Ticket#tags() to infer ticket status