Introduced the VariableNetwork describing the connections of variables/accessors before things get actually instantiated. This is needed to generate an XML file containing the published variables based on that information.

This is a first mock implementation with very limited functionality. The idea is based on discussions during the OPC-UA control system adapter kickoff meeting and subsequent personal discussions.

set required version of DeviceAccess to 00.12, since the build environment variables might have changed

git-svn-id: https://svnsrv.desy.de/desy/mtca4u/InstaCoSADev/trunk@2636 5f601a5c-88b9-47f3-b851-818f6741d00d

git-svn-id: https://svnsrv.desy.de/desy/mtca4u/InstaCoSADev/trunk@2635 5f601a5c-88b9-47f3-b851-818f6741d00d