Milestone 6 - semantic zooming

New:

• Dynamic loading works. Still some known (nut unresolved) bugs:
  • Edge thickness between subgraphs does not work.
  • SNPs do not work with dynamically loaded parts op the graph.
• View -> Toggle SNPs enables drawing SNPs as a single node.
• Clicked (or shift-clicked nodes are highlighted.
• Drawing performance improved by using a Canvas.