Add seamless tutorial

[chuck-sys]

Add a tutorial that only pops up once when you want to do things. Should make it pop up ...

1. At the start when we are on a blank canvas (prompt for A button press)
2. After adding a certain number of nodes (prompt for zooming in and dragging the canvas, if not done so already)
3. After we have deleted a node (prompt for deleting an edge)

Make it so that the state of the tutorial (done vs not done) is automatically saved in a separate localStorage variable. Also make sure that this is backwards compatible when we don't have this variable (at the start).

[chuck-sys]

For the second item, we could trigger it iff the user has a third of the screen filled up with nodes (by area). That way we could know exactly how full the screen is. Currently set up to trigger even if the user knows about dragging. Only triggers if the user hasn't used the scroll wheel to zoom in or out.