Collision detection when inserting and moving items #38

Features to be implemented:

• Do not connect to invalid items
  • Connector (Logicitem)
  • Linetree
• Do not anticipate invalid items
  • Connector (is_connected)
  • Linetree (edge indicators)
• Implement basic invalid painting for Linetrees
  • increase shape / bounding box for Linetree to Logicitem fraction
• Make invalid state depending on connectivity
  • output to output -> invalid (Connector)
  • two outputs driving Linetree -> invalid (Connector, Linetree)
• Update surrounding based on invalid bounding rect
  • InsertableItem move (single item)
  • Selection move (multiple items)
• Update inserting line to not collide with invalid lines.