Persisting connections

This change will make sure that connections that are activated between Endpoints can be persisted. This works as follows:
- During activation of the ConnectionManager, it will load the connections that should be activated and saves them. Any endpoints that are already active and are configured will be started at this time.
- When any endpoint is added and potential connections are detected, it will look in the configured set and connect it when it was configured.
- When any potential connection is connected, it will add it to the set and save the new configuration
- When any potential connection is disconnected, it will remove it from the set and save the new configuration

This seems to work for the testcase and when testing the connection manager UI.

@jankazemier can you verify that this works and merge it?