Remove gt.initGuider, allow one guider per tour at a time:

* Remove gt.initGuider completely (already deprecated) and its tests.
* Wrap guiders.resume in resumeTourFromId so we can ensure there is only one guider per
  tour at a time.  Use this wrapper for all calls.
* Add optional step argument to resumeTour.
* Add class to guiders, identifying which tour they're from.
* Add comment

Change-Id: Ibe7948184e3d3b4d2da233e858274dbd0b631a7e
Merge "Remove gt.initGuider, allow one guider per tour at a time:"