startController: add 'return to start location' feature

[moloko]

Most of the courses that we build which include an 'intro page' (or pages) have some kind of 'back to intro' button contained in them.

It would be handy if the startController module offered some way of handling much of the logic for you, something like:

Adapt.startController.returnToStartLocation(alwaysForce:Boolean, dontSkipCompleted:Boolean);

[moloko]

Just thinking: perhaps the arguments even necessary? I'm struggling to think of an example of when you might want alwaysForce and dontSkipComplete to be false? So maybe it should just be:

Adapt.startController.returnToStartLocation();

Thoughts welcome!

[oliverfoster]

Agree