Objects are sometimes partially outside the screen

[Robin_Z]

Objects are sometimes partially outside the screen which can only be resolved by zooming out.

[glenlow]

(In [191]) Fixed new nodes created to the upper left of graph not reachable (drawing board now allows negative origin coordinates, fix #110). Selections are now work in browse mode (fix #111).

GKGraph creation is now autoreleased.

Draw classes now integrate in-place updating, layer creation and management, instead in GKDrawAdditions categories. Text layers now cache displayed content until memory warning.

Main views and their controllers now communicate with delegates instead of notifications. Graph view now integrates autoscroll control, selection and tracing, instead of a separate select view. Better MVC separation: graph view controller now updates graph when notified, instead of graph view doing updates directly; graph view now responsible for resizing to enclosing scroll view, instead of graph view controller.