[Bf-modeling] Proportional Edit Mode (Connected)

[Campbell Barton]

To follow up on this topic, from the feedback so far my impression is
that PET currently works acceptably, minor improvements are always
nice but I didn't hear anything very urgent about PET failing or being
broken, or connected behavior being really annoying the way it is now.

Aside from Andy's comment about visualizing weight - I'm going to call
this `Good Enough`, and move on (in fact move back to mirror feature
discussed before).

Feel free to disagree and raise issues with PET - but think we can
move onto more important topics.