GH-108  Ignore skipped steps in numbering

Proposed solution is to keep track of skipped steps and use that info to adjust step numbering. This also takes care of saving skipped steps hash to cookie\localStorage for multi page tours.

Added unit tests for: 
  * numbering with skipped steps - going forward and back
  * numbering with skipped steps that are dynamically created
  * reading skipped steps from saved state