#1 multiple mailing list support

[Maurits Lamers]

MyCampaignManager now features only one mailing list per user. This is
quite unpractical.

It would be much nicer to be able to determine and save the mailing list
per campaign. It should display the e-mail address of the mailing list too
when asked for confirmation on sending.

These two features would make managing campaigns much easier and
better understandable.