Correct event name

We were attempting to remove a listener for the wrong event.

Correcting this exposes a design mistake: suppose the user pauses
the timeline, then moves the map, then presses play again. In this
case we would like the map to move back to where it was when the
timeline was paused.

However, now we have no way to even know that the map has been
moved while the timeline is paused.

The correct fix is probably to record the position at the point
where the timeline is paused, rather than when the map is moved.
Use a newer mapbox.js
Specify Talkie 1.3 explicitly
Remember map position when timeline is paused

This is a better way to do it, I think.
Move Talkie/Leaflet integration to its own file

Also bring in the trick I used on “In Flight” to interrupt map
animations if necessary, which makes the scripted view changes
more reliable.

(For example, if the user moves the map just before a scripted
view change, this will pause the timeline and register an undo
handler. When the timeline is resumed, the undo animation may
still be running when the scripted view change is reached, and
Leaflet will therefore just ignore the scripted view change.
This is not desirable behaviour. Explicitly interrupting the
existing animation like this makes it work as intended.)