Allow the definition of multiple phase events

Following the use case of the automated cars, we should imagine an interruption that is unexpected.

This means that we can imagine more than one type of interruption.

This has the consequence that a scenario will multiply its phase groups by the number of phase events.

Example:
A scenario with three steps and two phase event types will normally be executed in 4 phase groups, but now it will be in 8 groups

This applies only to ProCon phases.

## thoughts
Are the specific events global or specific to a scenario?

Start by locating the ProCon phase handling and the code that generates scenario phase groups. Clarify whether phase events are global or scenario-specific, then define how multiple event types affect the phase-group count. Done means a three-step scenario with two event types produces eight phase groups, with coverage for the new behavior.

Written by the indexing model from the issue text.