Divided model into two parts.

+
1. Model now consists of view-data (GraphScene with it's items) and
graph-data (GraphModel with QVectors).
2. GraphModel is comething that will be able to assign to list view and
table view. It has only graph-data, no visual. Just every item has a
pointer to it's other part of data so that it look like one.
3. GraphComment moved to QTextDocument of GraphItem, which is an
abstract class of GraphNode and GraphEdge.
4. GraphScene uses GraphVisNode and GraphVisEdge classes to store visual
data and to display it.
-
1. No property system working.