Fix next backlog date

Fixes next backlog date in API which currently uses 7 day cycle time regardless of config, Also changes display on UI which also used the 7 day cycle time as below:
Before:
![before](https://cloud.githubusercontent.com/assets/3397069/3423709/5a1ed436-ffa6-11e3-9ac7-fe083fa5e225.PNG)

After:
![after](https://cloud.githubusercontent.com/assets/3397069/3423712/5eaec894-ffa6-11e3-985d-f3b4bbfe4ac4.PNG)

I haven't altered the API to include a time as I wanted to ensure it didn't want it to break the compatibility with apps using the API - if you feel there is a low enough risk of it breaking anything I'm happy to make this alteration.