Manual Arrow draw feature (output only, maintain predefined structure, ugly arrows)

[michaelmarcuccio]

manualArrowPad option for enabling the manual arrow pad and connections feature. This allows:

1. joining two steps into single output
2. looping by going back to previous step
3. jumping to step in completely different part of workflow if you want

You can left click on the arrow to select it and then click the delete button that appears. These manually drawn arrows are NOT a part of the step's children. They are in another array below the root in the JSON.

{
  root: {}
  connectors: []
}

Dragscroll options now an array of choices for mouse button: ('LEFT' | 'MIDDLE' | 'RIGHT')[]

[michaelmarcuccio]

resolves #37

[michaelmarcuccio]

resolves #44

[michaelmarcuccio]

resolves #47

[michaelmarcuccio]

resolves #58