Messenger selection based on role/permissions

[Gawkky]

Since release 5.0.0 we can select the messenger per campaign.
This is a very exciting addition and I have an extra feature based on this.

So just like we have list-roles we could have messenger roles. I would take the list-roles setup and apply it to the messengers as that makes the most sense. These roles can see and send campaigns with these messengers based on their specific permissions. This will enhance user experience and prevents users to send campaigns with the wrong messenger.

[Gawkky]

If approved, I'll try to contribute myself of course.