BUG : do not add attribute if dimension is not 1 (scalars) or 3 (vectors)
BUG : corrected range issue when too small

- the rounding would be so that the min and max used (not displayed) would be egal for small values, so no possibility to have different values between them
BUG : modif vectors in updateAttribute_QT for fibers

- for fibers, there can be no vector fields. Therefore we can't be looking for a vector attribute to display in the combobox. Our solution is to look for them after looking for the scalar attribute.