Message queue for communication between AppDomains and Threads

[kgrading]

The message queue should be implemented as a List, containing MessageContainer Objects. A MessageContainer Object consists of 2 Parts: The actual Message (will be implemented as a Enumerator called MessageType) and an additional ID.

The ID is used for additional identification purposes (e.g. The message is something like GetFinishedJob and the ID would be the id of the execution engine, sending this request)

The list should use a synchronization mechanism (e.g. a semaphore) that blocks the core thread, when no more messages are available for processing. Additional locking should not be necessary due to the fact, that there is only one consumer.