do not read initial values in TestFacility if testable mode is disabled, as this is subject to race conditions then

allow using the TestFacility without the testable mode, which can be useful for some tests of the framework itself

- treat the two directions of bidirectional variables properly in testable mode (i.e. as individual variables with each one counter)
- fix a data race in testable mode in case a bidirectional variable rejected a value (was not holding a required lock)

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

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

Cache accessors obtained through TestFacility::getScalar() and TestFacility::getArray() by the application test code, to avoid the loss of the current value if a decorated accessor is obtained again.

detect stalled tests and print a list of variables which contain data not processed by the application

- updated the tests for the testable mode and test the TestFacility class there as well