Reference Redmine

• Made plugin ignore references to issues of closed projects

This prevents the plugin from adding journal entries to referenced issues that belong to closed projects, partly solving #5 for specific use-cases. Note that the Bitbucket link will still create links to the issues in Bitbucket.

• Added a migration to change the user type to User

This makes the name of the Bitbucket reference user show up in the journal entries. I.e instead of "Updated by Anonymous" it now says "Updated by Bitbucket reference".