refactor(dia.LinkView)!: remove support for legacy link view

[kumilingus]

Description

Remove support for legacy features of joint.dia.LinkView (It has long been deprecated due to poor performance caused by built-in link tools that had to be rendered for each link at start-up (even though they are only visible when the user hovers over them).

• joint.dia.Link has no markup defined and effectively becomes an abstract class
• drop support for semantic string markup (connection, connection-wrap, marker-source, marker-target, marker-vertices, marker-arrowheads, link-tools in the markup has no longer effect on the user interactivity).
• drop support for vertexAdd, vertexRemove, vertexMove, arrowheadMove, useLinkTools interactivity paper options
• the following protected methods has been removed for LinkView: dragConnectionStart, dragConnection, dragConnectionEnd, dragVertexStart, dragVertex, dragVertexEnd
• the paper defaultLink is now standard.Link

The linkTools.Vertices tools now accept 2 new options: vertexAdding and vertextRemoving

Migration guide

Switch to joint.shapes.standard.Link and add link tools dynamically.

For the interactive options:

• vertexAdd, vertexRemove & vertexMove - add linkTools.Vertices to enable the user to interact with vertices

  new linkTools.Vertices({ vertexAdding: boolean, vertextMoving: boolean, vertextRemoving: boolean })

• arrowheadMove - add linkTools.Arrowhead to enable arrowhead move

• useLinkTools - add linkTools.Button to the link view