New Connection Editing System

[Seneral]

For supporting Multi-Multi connections (connections between two knobs with MaximumConnectionCount.Multi), we need a new way of editing connections.
The current system relies on one knob with only one possible connection to delete the connection and the other one to create them, which is suboptimal.
Consider this a continuation of #74 to adress #144 and #145 and fix #147 and #148.

New concept for ALL connections:

• Create new connection by dragging from any of the two knobs to the other.
• Delete multiple connections by holding a key and dragging a 'cutting line' to delete (cut) all connections under the line (see https://youtu.be/XKbSu5PC8VA?t=633 from How to remove connections when using ConnectionCount.Multi? #145)
  OR
• Delete single connections by right-clicking them or similar.
• Preview connection values for ValueConnections and perhaps select connections (important for some kind of connections that have own behaviour/conditions).
  This requires hit detection between point/bezier and/or line/bezier.