[GNC-dev] openSUSE added to Docker; easy builds for dev and CI

[Dale Phurrough]

Hi all. I've updated the Dockers to build Gnucash for openSUSE 5.0 and 5.1.
https://github.com/diablodale/gnucash-dev-docker
With these, you can build GnuCash 3.5+ on major releases of Ubuntu, Debian,
Arch, CentOS, and openSUSE Linux.

These are great for continuous integration (CI) by everyone by unit testing
your code and integrating them into systems like Travis. Also good for new
dev/testers and seeing how to setup your computers with all the needed
dependencies to compile.

   - Windows: Blocked due to bugs in the Gnucash-on-Windows project.
   - FreeBSD: The Docker project on FreeBSD died. I won't be delivering
   these.
   - Fedora: coming soon...

--Dale