Non-readonly Properties should be stored and restored in the next session

[Kittyfisto]

Now that several options which were previously handled in IDataSource are about to be moved down to the ILogSource and be handled as IProperties, there needs to be a serialization strategy in place which supports both well known properties (those delivered by Tailviewer) as well as properties introduced by plugins.

The latter probably requires an interface extension of some sort to look up how to serialize and deserialize a property.