Use proper iteration ordering in decorator.
Rewrite factory for burndown with metrics
Use burndown#current_iteration in the decorator
Use burndown#current_iteration in cucumber steps
Move iteration responsibilities to Iteration
Merge pull request #24 from kabisaict/fix_decorator_with_iterations

Refactor Iteration responsibilities.

Things like iteration start and finish dates and generating iteration JSON data are now handled by Iteration instead of Burndown.