[GNC-dev] centos-7 Docker ready - clean compile of Gnucash 3.5 on Centos 7 no hacks

[Dale Phurrough]

Hi all. I've added a centos-7 dockerfile that will cleanly compile GnuCash
3.5

https://github.com/diablodale/gnucash-dev-docker

The Centos-7 Dockerfile adds the well-known EPEL repository. This
repository is needed for common components like Aqbanking and libofx. Given
that repo is available, I leverage it for Python36 and Boost1.69. The
latter is the only available version of Boost that meets the GnuCash
project requirements (without downloading and compiling Boost itself).

I now turn my attention to a *Windows* Docker container. This will enable
me and anyone else to easily spin up a container to develop and compile
Gnucash on Windows. :-)

--Dale