ui.resizable should be able to preserve the aspectRatio

The ui.resizable should be able to preserve the aspectRatio.

I think the best way would be to allow different kinds of aspectRatio preservation:

• If no option is specified and the SHIFT-Key is pressed during resize, the aspect ratio should be conserved.
• If let's say "aspectRatio == 'preserve'" then the aspectRatio should be calculated from the resizable element's original size and be preserved.
• If let's say "aspectRatio == 1.5" an aspect ratio of 1.5 should be forced on resize, even if the original resizable element's aspect ratio was different.

All in all the preservation of the aspectRatio should behave like we all are used to from e.g. photoshop: Dragging the E-handler resizes the resizeable to top and bottom, dragging the SE-handler resizes to bottom and right, etc. pp.

Optionally adding a functionality to the ALT-key could be a nice feature: Then, not the opposite drag-handler should be the point of reference for the resizing but the center of the resizable (i.e. dragging the S-handler resizes to both, top and bottom, not only towards the bottom).