makes test move_invalid pass

- Implemented but not tested yet
- All existing tests passing

* Not implemented yet. Currently always return false.
* Test exists and compiles, but is failing due to the missing implementation.

- All variables conceptually have an initial value now.
- All initial values read by blocking read() before starting the main loop.
- More tests failing, probably to old test exceptiations and wrong test implementations.

- tests still failing
- modifications incomplete
- cleanup needed

fix not using a ConsumingFanOut when connecting the two poll-types each with a push-type variable (e.g. control system)

this happens frequently when following the modern connectTo() logic and connecting everything with the control system.

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.

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

Use one file per class. Also, use boost::core::demangle instead of
checking for abi::__cxa_demangle by ourselves.

We have a visitor now for generating
 - the XML
 - the Module's dot graph
 - the textual dump of the VariableNetwork
 - the dot graph of the VariableNetwork