Add ability to add a default Jira instance

I would like to be able to define a global default Jira instance so that I don't have to know the id of a configured Jira instance in order to use the Jira Macro.

A dropdown in the Macro would also be cool. But the easiest would be to add a checkbox to the configuration to state that this instance should be used if no other id has been supplied to the Jira Macro. Could also be to add an instance with blank id or "default" as the id....