Fix T41467: Modifier view buttons changing positions.

Commits early in this year (to save some space) broke this. Hopefully this time
it works in all cases - lastCageIndex is no more influenced by realtime/edit active states.
Also, inactivate buttons instead of hiding them, can be useful to set those data
even though it does not have any immediate effect.

Took the opportunity to switch cage buttons to RNA, btw.
initial intersect code
initial isect
intersection script
test vert intersection
check for intersections where no new verts are added first
minor fixes
WIP
add vert-edge check
Print info
De-duplicate - dont add same verts to edge multiple times
Dissolve
Dissolve based on tags
improve intersection dissolve
Dissolve now works
WIP
WIP
WIP
WIP
WIP