[WIP] Add option to clean scheduled messages on startup

[kenliao94]

Working in progress: add an option to delete all scheduled message on startup.

[kenliao94]

Hey @mattrpav and @jbonofre I am curious on what you think about the approach here and want to clarify a few things:

1. I was debating between adding this logic to the job scheduler or the persistence layer (following the approach of deleteAllMessages). However, I noticed that SchedulerBroker doesn't expose their internal scheduler, and it has public methods that deal directly with Message (initially I thought SchedulerBroker is not "message aware" but only "job aware". So I decided to add the logic in SB. What do you think?

2. I wasn't able to find any other non-message jobs (even job in ByteSequence type is assumed to be unmarshal into Message) scheduled on "JMS" scheduler so I assume that remove all jobs are safe. However, do you know any pitfull for simply remove all jobs?