Mesh “point of view” selector is confusing

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The mesh plugin has a radio button family with three options: “Display
all points”, “Current view”, “Share viewpoint”. Their effects seem to
be:

• Display all points: On selection, immediately changes the camera for
  all mesh views.
• Current view: Does nothing?
• Share viewpoint: When a mesh view changes camera positions, if this
  option is selected, all other mesh views snap to match the new
  camera position.

It would make more sense to have a single push-button “Display all
points” (or “Zoom to fit”? to make it clear that we’re not actively
hiding points otherwise) that resets the camera for all meshes, plus a
checkbox “Share viewpoint”.

Also, checking the “Share viewpoint” box should immediately align all
cameras, because (a) it shouldn’t be possible to be in a state where
“Share viewpoint” is checked and yet the viewpoints are not shared, and
(b) a small perturbation of the camera should always be a no-op rather
than discontinuously adjusting all other cameras.

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cc @podlipensky; let me know if you’d like me to assign this to you.