Implement callout and tour lifecycle events

[kate2753]

Add support for previously supported callout\tour event callbacks: onPrev, onNext, onShow, onStart, onEnd, onClose, onError.

• Address tour-wide callback doesn't get called if there is a step callback #113
• Address getCurrStepNum() returns 0 when called from onEnd callback. #158
• Address Pass along captured browser event to Hopscotch callbacks #191
• Address Callbacks on callouts do not work (registerHelper or listen) #97

[timlindvall]

As part of this, we should look towards making these events deferrable (probably using .then() syntax, though this is TBD). Doing so should resolve #231.