StackOverFlow when restoring TeiidServerManager state

When starting designer with a saved server model, the TeiidServerManager is restored. However, 2 types of stack over flow exceptions can occur.

ModelerCore makes the init of the manager thread-safe by surrounding the construction with a synchronized object. However, this does not prevent the same thread calling it. This can occur when the newly constructed TeiidServers call their disconnect method, which uses the manager to notify any interested listeners.

First, the use of the manager here can mean the potential creation of a second manager, looping ad infinitem. Fixing this in ModelerCore, then has the difficulty that the single 'restoring' manager tries to notify the interested listeners. If such listeners have already been assigned, eg. PreviewManager, then they can start trying to use the manager illegally before its completed restoration.