Rotate and Delete from the ground up

[hchiam]

follow-up to PR #657 (closes #657)

fixes #613

• [x] create a new visbug-rotation handle-like element
• [x] write your own pointer down/move handlers
• [x] ~add new handle into handles~
  • [x] added both <visbug-rotation> and <visbug-delete> into selectable
• [x] create a visbug-delete element