Extend NoParallelExecution for all Triggers

[michaelschnyder]

Current Situation
The current implementation of NoParallelExection only guards the parellel execution if the trigger is a "Scheduled" one. That means, that a Job with a Trigger and NoParallelExecution set, does still allow running the job at the same time but with a different trigger.

Proposed Change
The NoParallelExeuction should be set on Jobs and not in a single trigger instance. The aim is to exclusively run one single instance of a job no matter with trigger or triggertype has scheduled the run.