Feature request : Rectangular and Oval gradient and masks

[pierrelabreche]

For the Oval gradient transformation and for masking with rectangular and oval shapes, the ability to :

• Center the shape on the image
• Define the shape by distance of the shape bounding box to the image border ( linking the top, bottom, left and right margins )

In addition, for masking with rectangular and oval shapes, the ability to :

• Snap the angle to multiples of 15 degrees ( by holding down Shift )