Merge "Modeling workbench console" and "Execution Engine" consoles

In GEMOC, thanks to the messaging system, it is relatively easy to have dedicated eclipse consoles.

However, we end up now with 3 consoles:
- the "default MessagingSystem console" that collects every System.out System.err message. This console is handy for quick and dirty messaging, but it gets polluted by messages from every plugins in the eclipse installation
- the "Modeling workbench console" currently gets the start and initialize notifications from the ALE engine
- "Execution Engine", currently gets "Execution finished" and "Exception in Addon" messages

possibly one DSL developper may also wish to have a dedicated console for her DSL (ie. isolate from other DSLs).

I suggest to remove the "Execution Engine" console (by redirecting all messages to the "Modeling workbench console")

and encourage DSL developers to either use the "Modeling workbench console" by default (or use their own console ) instead of the System.out. This would be done by updating the official example in order to show how to access these consoles.