Support the instanciation of pipelines - have a proper pipeline loader

[lhubert]

Expected behavior and actual behavior.

We want to be able to run pipelines in multiple environments (Spark, Flink, Java bare metal in an application). At the moment the pipelines use class loaders that make instantiations difficult. We should introduce the concept of pipeline and provide a loader that give us more flexibility in running our pipelines in different situations.

Steps to reproduce the problem.

Specifications like the version of the project, operating system, or hardware.