ENH : alignment of meshes updated

- When you were selecting multiple meshes, the first one selected was being reseted because of the Original/Centered Option. Now, you can not have meshes in Original position and meshes in Centered position at the same time : the position is the same for all meshes.
- This modification helps correcting the unwanted reset, simplifies the aligment tool, and therefore simplified the code by deleting the alignement verification at any selection.