Inverse repository now subscription only

[mikesager]

This is an FYI as much as anything. Inverse has made the SoGo repository subscription only. Your Dockerfile fails now as a result. I'll leave it up to you whether to add username/password support for those who have the $$$$ to buy a subscription or if you want to use an independent repository. One user has graciously compiled the packages and provided a public repo (https://lists.inverse.ca/sogo/arc/users/2016-07/msg00172.html). Maybe the Dockerfile should just be changed so the user provides the repo URL at run time.

Anyway, thank you very much for your work on this container. Take care.

[mikesager]

NB: If you use the user-supplied repo I linked to in the article, it places the Apache SOGo.conf in /etc/apache2/conf.d by default. I had to update your apache2.sh to reflect the change. You can look at my "reposwitch" branch for my changes, but as of the time of this posting, I haven't tested it yet beyond building the image and starting it to see if the files were copied properly.

[mc0e]

Seems like a good idea to me. Pull request?