Cannot use message service before workbench is up

[weinand]

while testing #9690:
The 'take feedback survey' does not show up because it is posted too early.
Forcing another notification some time later, brings up both notifications.

[joaomoreno]

It all boils down to this indirection which decouples the message list with the construction of the workbench. The MessageList can't know when the workbench is finally ready due to how we set up the whole infrastructure, so it just drops messages.

Had to push 5418b6c in order for it to work.

The DOM construction of the workbench should happen in its constructor. That way we don't need to have global IDs laying around and base widgets looking around for them...