New VO + All Levels Scaffolded

@kadst43 @ajiraffe @BrettASwift Ok so there's a bunch here so it'd be good for everyone to take a look. Adam I think I might have lost a bit of the new alert/orbit functionality at the end of level 2 during a rebase so could you pull it down/check/commit it back if I did? The equations for navigating the canyon (since there are no tracks) are x/-2 x/5 and 7x/3 ... I will send an email with images of where you should end up/which blockly programs to use and where these "track anomalies" should be in the terrain. The sensor is a bit of a hack but short of supporting some sort of way to represent/read tracks on a grid I figured detecting turns ("anomalies" which lets us also detect the end of the track/the rover) was a good start. The loop 3 times stayed in for now, still have to talk to Juan, but in playing I found it was a good reintroduction to the idea that "hey this thing is going to happen a few times" before giving them a totally unfamiliar block. Currently intentionally replaying the hint VO for each subscenario of level 3... can easily be removed. Let me know!
Just `showAlert` to come back here, with the exchanged string parameter.