Added new methods getBoundThings and getBoundChannels to ItemChannelLinkRegistry.

Signed-off-by: Dennis Nobel <d.nobel@external.telekom.de>
Changed to new HashSet<> instead of using Guava.

Signed-off-by: Dennis Nobel <d.nobel@external.telekom.de>
Merge pull request #64 from qivicon/itemchannellinkregistry-additions

Added new methods getBoundThings and getBoundChannels to ItemChannelLink...