Centos6 Dockerfile for testing minimal development requirements

Used for checking what our build requirements actually are since they're not documented in a single place
https://github.com/openmicroscopy/ome-documentation/pull/954

Once this container is built it should be possible to start a shell, checkout the openmicroscopy source, and execute a full build using `docs/hudson/OMERO.sh`.

This probably shouldn't be merged since we should have some proper development/build Dockerfiles on the way, thought I'd open it in case anyone wants to take a look.