Start using CI servers for building application images

[onnimonni]

In order to achieve more reliable deployments we should stop building stuff on the same servers where we run our software.

Here's one good example with multiple errors:

We could have more beefier CI servers running the builds. CI servers could build complete application images which are then deployed to dev/staging/production servers. This would make dependency management much more easier too and we could easily rollback everything including changes to php versions.