Fix jitter when resizing explorer sidebar on Matrix vis

[axelboc]

This fixes two jittering issues when resizing the explorer sidebar:

• Some control labels would sometimes wrap onto two lines. I noticed this with the Cell width control on the Matrix vis, but the same could most likely happen with Selector labels. I now prevent wrapping in both cases.
• The Matrix visualization would overflow and cause sidebars to appear and disappear quickly.

BEFORE	AFTER

[loichuder]

Nice !

[loichuder]

I wish this would have been merged before the demo last week 😂