Adaptive control point positioning to prevent a cusp.

(transplanted from orage/2ec166afa6771d78ff3b62f8ee339ad5516c7a89)
Added 'statusMessage' property to the widget/node.

(transplanted from orange/49a8be8076a9ed724cfcead2d1f3cebe33b407d8)
Added three demo widgets and a widget template to documentation
Cleanup of itemmodels.py
Merge remote-tracking branch 'upstream/master'