Heptapod PAAS Runner prototype, second iteration

The first version of the prototype was not committed here and was only able to grab one job and launch it on Clever Cloud.

This one is able to run permanently and launch jobs in parallel.

It is fully covered by unit tests, because we want it to evolve towards production status, and we need to make changes safely while testing it on foss.h.n. Also the feedback loop for real life testing of changes is especially high.