bidirectional variables: pass on version numbers in modules from the last blocking read on to any write operations, to resolve conflicts of concurrent variable updates properly

fixed testable mode for bidirectional variables: the return channel of control system to application variables must not increment the testableMode_counter

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

fixed bug that using poll-type transfers in testable mode could sometimes lead to stalled tests or assert failures.

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

preparation for future changes: The TestDecoratorRegisterAccessor now gets a ProcessArray as argument, not the more generic NDRegisterAccessor. This allows it to use specific features of the ProcessArray.

- delete the copying operator=

fixed race condition in testable mode: now stepApplication() will use a semaphore counter to ensure that all processing is done

implement the "testable mode" in which the application can be paused and resumed by the test routine

Added a TestDecoratorRegisterAccessor which is optionally put around accessors to facilitate test of applications. This TestDecoratorRegisterAccessor does not yet do anything, functionality will be added in the next commits.