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)

extend test of bidirectional variables to include plain direct Application to ControlSystem connections (no FanOut etc. involved)

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

extended the test to make sure also the "observer" variables in the control system show the right values

- 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.

Unfortunatly this currently breaks the ServerHistory module, as it relies on slashes in accessor names. The MicroDAQ module had the same issue but has already been fixed. This fix can be adopted to the ServerHistory module as well.

Fixed wrongly created hierarchies when directly connecting a device to the controlsystem using connectTo(). Now proper virtual submodules are created for each hierarchy level, insted of keeping the slash in the variable name.

fixed connectTo() for direct device to control system connections when using the [] operator on the device module