Comment 6 for bug 689792

Description from duplicate bug entered by Charline after conducting the Natty user testing:

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Usability testing has shown that participants misinterpret the semi-maximise and maximise gesture previous shadow as a warning to stop their action. They do not understand the correlation between this gesture preview and semi-maximising and maximising the window.

Desired solution:
- implement the maximise and semi-maximise transitions as illustrated in the animations provided by design.
- see https://chinstrap.canonical.com/~johnlea/transitions/1104unity_elements/maximise_gesture_preview.mov
- see https://chinstrap.canonical.com/~johnlea/transitions/1104unity_elements/maximise_gesture_preview.mov
- This gesture preview does not need to be live. A cached snapshot of the window can be stretched as a performance optimisation.