FramesDisplay axes keep growing in certain cases when rotating a single frame at the origin

[iamtesch]

Noted/added in PR #47

The 'never shrink' mod works well with an arm where origins move around, but something weird happens when doing just orientation where the box keeps growing and growing in some directions depending on how the the frame triad is oriented.

[daverolli]

Patched for now by allowing the user to set fixed axes sizes. But it would be nice to figure out a real fix at some point.