Changing node shape should also change node style, not set the default node style

[jp101@…]

1. A default style is set for a node (say a square).

2. An attempt to create another square node is made but the sketch is recognised as a rectangle so the default style for a rectangle is correctly applied to the node.

3. A successful attempt to draw a square over the incorrect rectangle is made, however the square style is not applied but the existing rectangle style is retained and the square default style is changed to match that of the rectangle.

Should be:

A node should change style based on its shape and should not inherit the style of a previous shape.

[glenlow]

(In [145]) Changing node shape now applies default style, instead of recording default style (fix #91).