Implemented first part of #17: A HierarchyModifier can now be specified instead of the eliminateHierarchy boolean flag. No new functionality is yet added.

- reformatted source code

- added more comments
- need to catch exception by reference, else the message seems to be lost
- test if the message is correct
- test if device is really closed and opened again
- changed names of status variables in control system to match the general naming conventions

Do not try to make consuming control system variables bidirectional. It was running into an assertion and anyway makes no sense.

do not create TestableModeAccessorDecorator for unidirectional PVs with both directions enabled (was hitting an assert)

- 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 bidirectional direct application to control system connections (without any FanOut in between)

Fixed getCurrentVersionNumber() and setCurrentVersionNumber() so they always get/set the version number of the ApplicationModule and not e.g. of a VariableGroup.

- implement ThreadedFanOut version with return channel
- add test for ThreadedFanOut with return channel

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

Implemented bidirectional process variables for control system variables. There are still bugs and the test is failing...

Added preliminary support for bidirectional variables. There are still some known issues, e.g. concurrent updates can still lead to race conditions. This will be addressed soon.