Update old links and revise page content

I was doing some editing on the Wikis and stumbled across a page which introduced the kdemail.net e-mail alias system which sounded quite useful. Sadly though, the link to open a ticket with the Sysadmin team requesting one was broken. Sensing an opportunity to make a quick contribution, I updated all the links and revised the content of the page in the hopes of making it more inviting and informative to new contributors (which I, myself, happen to be). Hopefully I didn't get too carried away, but please advise if that is indeed the case.

I'm happy to revise my efforts and realize I have a tremendous amount to learn still about software development in general and the KDE rubrics in particular. My thought is that if/when this MR has landed I'll not only be submitting my request for a kdemail.net address correctly and to the appropriate people, but I'll hopefully have earned it as well.

Cheers, Peter