fixed logic in combinational choice from
fixed model running state (UI) after execution error
added validator check for patterns - tracing is for newly created resources only
added new Traceable interface
added ResourceStructure class (name's self-describing)
first adequate tracer (#12) implementaton
resources are now traceable (#12)
tracer (#12) instance in simulator
tracer registration for resources in database (#12)
resources are now being traced in patterns' converters (#12)
fixed resource retrieval bug in expression compiler

resources should have fully qualified names now. these changes were made along with previous commits