Initial contribution of thing concept.

Bug: https://bugs.eclipse.org/bugs/show_bug.cgi?id=433994
Also-by: Oliver Libutzki <o.libutzki@external.telekom.de>
Also-by: Kai Kreuzer <k.kreuzer@telekom.de>
Also-by: Michael Grammling <m.grammling@external.telekom.de>
Signed-off-by: Dennis Nobel <d.nobel@external.telekom.de>
If possible, it would be great to separate thing and thingtype classes - a new core.thing.type package should be created. It is clear that we would need a new ThingTypeRegistry in order to decouple meta data from instances. If the core.thing package is afterwards independent of core.thing.type, it would be perfect.