Rewrite operator to use k8s states

This MR introduces structural CRDs, CRDs now have states (executionState, duration, age). These states are used by the controller to decide which execution should be executed.

This MR reacts only to changes of execution crds, also only exections have a status.

In particular, this MR closes the following issues:

• Closes #223 (closed)
• Closes #190 (closed)