Refactory IterationDecorator spec
Return JSON for entire iteration length

If an iteration takes 2 weeks, but you're only
3 days into the sprint, Iteration#to_json will return
14 metrics, the first 3 filled, the last 11 filled with
zero values.
Merge pull request #23 from kabisaict/23_show_all_days_in_iteration

Show all days in interation