They are torn down on program exit (retracting all live IUs)

* Exceptions when trying to modify retracted IUs.
* Removal of IU also retracts it.

Manually integrated the following changes from b8466a (master 2015-11-13)

- Blackboard classes by hvanwelbergen
- Blackboard test by hvanwelbergen
- Payload merge fix by hvanwelbergen
- rsb Buffer fix (by myself) copied but inactive (not needed atm?)

Please refer to the logs of the legacy-str branch for a full history
of the respective changes.

(by ignoring nonexistent keys)

(for remotely triggered local-IU handlers, in order to let the
RPC call of the remote side succeed as it should).

ipaaca-python: It's now possible to specify a single string category interest on InputBuffer instantiation.

Added ipaaca channel possibilities based on rsb scope. Also, deprecated incompatible InputBuffer constrcutors for non-container parameters for multiple categories, from cpp version