Add Parameter for Unique Values

[WillFreitag]

When testing Orion Context Broker's subscription, it might happen that some of the messages sent are not notified (e.g. QuantumLeap), since there is no change in value (i.e. sending the same value for an attribute twice).
If it's necessary to have 1000 notifications when sending 1000 messages, the user will use the new parameter and that will result in unique values per attribute.

• Add Parameter
• Implement synchronized value store (per Attribute)