Fetch lists by role to avoid seeing 'nonmember' lists.

The latest postorius master introduces a new authenticated index which shows lists that the user is subscribed to, moderates, or owns. However it also (I believe unintentionally) shows lists to which the user is a 'nonmember' (as in, they've participated in a discussion, but are not subscribed). This is because a call to 'lists/find' without specifying a role will include the users "non-memberships". This MR makes it such that when no role is specified in the drop-down, postorius will make three calls to 'lists/find' (one for each valid role). Not sure if there's a cleaner way to accomplish this.