Sketcher RestoreInternalAlignmentGeometry

Description
The command deletes unused elements aligned to internal geometry, or recreates the missing ones.

How to use
If there are free alignment places for the selected element, new construction geometry is created and aligned to the available places. If all alignment places are occupied, the unused internal geometry is deleted (the element is treated as unused if it is not constrained to anything else).
 * Select an element of a sketch that supports internal alignment (currently only Ellipse/Arc and B-spline).
 * Invoke the command by clicking a toolbar button, picking the menu item or using the keyboard shortcut.

Example
Create a new ellipse. New ellipses are always fully-packed. You'll see an ellipse and a bunch of construction geometry: major diameter, minor diameter, foci.

Select minor diameter line and hit. The diameter is gone, but the ellipse remains. How do we get the diameter back?

Select the ellipse and invoke the Sketcher_RestoreInternalAlignmentGeometry command. The diameter is restored.

Now, constrain the major diameter of the ellipse to some length. Select the ellipse and invoke the Sketcher_RestoreInternalAlignmentGeometry command. Minor diameter and foci are deleted, but the major diameter is kept, because it participates in other constraints. Ellipse's center remains too, because it is inherent, like center of a circle.