Add option to stop a plug-in from beeing executed by the internal job queue

[Nicklas Nordborg]

Currently you have to choose if you want to use job agents or the internal job queue. If you use both all jobs may run on the internal job queue even if you have configured job agents for a plugin. An option that stops certain plugins from using the internal job queue allows an admin to use the internal job queue for plugins that don't need the overhead of a job agent.

[Jari Häkkinen]

Milestone BASE 2.4 deleted

[Nicklas Nordborg]

(In [3871]) Fixes #595: Add option to stop a plug-in from beeing executed by the internal job queue References #746: Moved plugins/jobs section to docbook