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>
Should be moved to the internal package and the Thing interface does not need add/remove methods for it.