[feature] Docker support

[viyatb]

Vulnreport is based on a Ruby-stack, and it requires a clean environment to deploy to. A docker image can ease the deployment of the application (as compared to a new VM) along with shared volumes with the host so that pentest data and report can be easily exported.

[littledatas]

Working on this now. Stay tuned!

[noraj]

Would love a docker too but it seems the docker branch didn't move since 2017 and also dependencies are broken (#32) and need to be fixed before building a docker.