Redmine

I've updated the Redmine installation documentation at the following links:

• https://www.redmine.org/projects/redmine/wiki/HowTo_Install_Redmine_on_Debian_9
• https://wiki.debian.org/Redmine

My focus is using official packages for long term support and stability, I also re-formatted and simplified the steps for installing from sources.

Any comments and suggestions are most welcome.