Improve selection handling

[paullewis]

This is going to take a rewiring of selection states within the editor.

Things that need to be supported:

• Selection of items (including Ctrl/Cmd + a)
• Deselection of items
• Drag movement of all items in the workspace
• Storing of item location after move
• Deletion of items
• Ctrl/Cmd+x to cut
• Ctrl/Cmd+c to copy
• Ctrl/Cmd+v to paste
  • Graphs
  • URLs
• Reset graph location
• Drag and Drop from Components panel
• Auto-selection of pasted & dropped items
• Handle disambiguation of edges
• Bring back comments
  • Check comments work in terms of dragging etc
• Clean up old events and logic
  • Editor
  • Graph Renderer
  • Graph Node
  • Graph
  • Events

[paullewis]

Declaring victory.