Refactored ManagedThingProvider#createThing and
ThingHandlerFactory#createThing in order to pass a ThingTypeUID instead
of a ThingType

Signed-off-by: Oliver Libutzki <o.libutzki@external.telekom.de>
Added some Javadoc

Signed-off-by: Oliver Libutzki <o.libutzki@external.telekom.de>