Virtual points do not change rigid body transformations

[Ariel]

The rigid body transformations of a bone are identical before and after adding two virtual points. The virtual points appear to be moving correctly in the video window, but do not match up with the dashed lines meant to connect them to the rest of the rigid body.

(virtual points and rigid body are in yellow in the attached screenshot)

[Benjamin Knorlein]

fixes #135 : Virtual points were not completely cleared

→ <<cset 70d6528b72f9>>

[Benjamin Knorlein]

fixes #135: Final fix 2D-3D optimization also uses virtual points. In addition some other stability fixes.

→ <<cset 418da9890a16>>