inspector: graph: use anchors instead of buggy Layout.alignment
inspector: qml: MarSystemAdaptor: declare some properties constant
inspector: qml: MarSystemAdaptor: add "hierarchical level" property
inspector: graph: reintroduce color-coding based on hierarchical level
inspector: RealvecWidget: increase size hint and use expanding policy
debugger: separate current state recording from debugging
inspector: support displaying system input/output via MarSystemObserver

* Refactor to expose DebugController - a new class interfacing with
  the "debugger" class

* Use MarSystem processing data collected by DebugController
  (internally consisting of a MarSystemOberver), as source for display.