fixed a potential invalid read/write error, access to object and its potential destruction was done in wrong order

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.

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

Changed an exception into an assert, since the function is only internally used and the exception is never thrown. Clafiried the documentation about this.

When optimising the connections (i.e. merging networks), the trigger receivers for triggered networks are now removed from the trigger network. This was previously leading to crashes.

renamed VariableNetwork::addTriggerReceiver() into VariableNetwork::addNodeToTrigger() for better clarity

fixed using out-dated strstream, fixed dump() which was not passing the stream to dump into on to internal calls of VariableNetworkNode::dump()

Made some exception descriptions more elaborate. To achieve this, the dump() functions have been extended to allow writing to an arbitrary ostream.

Rebased the ScalarAccessor and ArrayAccessor classes onto the mtca4u::NDRegisterAccessorBridge class.
Known problems present: code compiles but tests do not run

Fixed a bug that a pointer to a temporary VariableNetworkNode object was sometimes stored (as a trigger receiver or source). Instead now an object with the same data pointer inside is stored.

Adapation to the unified versions of ControlSystemAdapter and DeviceAccess.

Status: Library compiles, tests do not yet compile.

- extended the trigger tests
- removed some debug output

Introduced the DeviceModule class which provides an interface to obtain VariableNetworkNodes for device registers

- performed some code cleaning and refactoring
- store all nodes in a VariableNetwork in a single list, to allow deciding later if a node is feeding or consuming

This commit is an intermediate commit and has known bugs. Almost all tests are failing and the demoApp is not running. Debugging will be done in a next step.

introduced an operator>> and operator<< syntax to connect network nodes. to realise this, the VariableNetworkNode class has been changed into a pimpl pattern.

Allow to make connections directly based on VariableNetworkNodes. This is a first step, more changes have to be made in this direction.