necessary changes for the latest DeviceAccess update (readAsync() return type no longer a reference, and other related changes)

update for interface change in DeviceAccess: TransferElement::write() has now the version number as an argument

- use this return type in testable mode to detect when a queue overflow happened (testable mode counter should not increase in that case)

use the new readLatest(), which has been added to the latest DeviceAccess version, to implement the naturally expected behaviour when using a push-type variable with a poll-type accessor

Changed the FeedingFanOut so that it does not extract the meta-data (name, shape etc.) from the first slave but expects it in the constructor. This is necessary since the meta-data is already given by the application.

- add all networks triggered from the same node to the same TriggerFanOut
- put all feeding nodes in a TriggerFanOut into the same TransferGroup

- added some class documentation