Generate financial report with date range

Added category field in bill table
Added categories when creating new bills
Added financial report component

Complete report
![completereport](https://cloud.githubusercontent.com/assets/3430891/5306516/065fd9ea-7bd3-11e4-8116-2d795f47cd5f.PNG)
Partial report
When transactions only occured in some categories
![partialreport](https://cloud.githubusercontent.com/assets/3430891/5306517/089382fc-7bd3-11e4-950e-2b4387da87b5.PNG)
No result
When no transactions occured in date range
![noresult](https://cloud.githubusercontent.com/assets/3430891/5306518/0a9457e8-7bd3-11e4-8dd1-bb9ea65d841e.PNG)

why is this empty ?