Constrain behavior for expansion/contraction of mesh

[kephale]

@kevinyamauchi and I discussed this earlier in the week: we should have a tighter range on the expansion/contraction range, but allow the user to expand the range (similar to the current behavior for contrast limits in napari)

[kevinyamauchi]

For reference, here's the contrast slider on the napari image layer: https://github.com/napari/napari/blob/9dd5fd2d0e12a99973a482bb775597e2176e17ca/napari/_qt/layer_controls/qt_image_controls_base.py#L95-L96