added d3 and nvd3
changed data format to fit nvd3 stacked chart
added test scenario where boards are empty
filter lists relevant to sprint
changed chart to stacked bars
changed chart configs for improved visualization
changed checkitems to filter cards with points and include total checked items
changed assets config to enable assets on heroku
adding gem for heroku
added title
refactored checkitems methods to delegate only_points option to cards
changed checked count to substract initial checked items on start time
extracted query to method
Merge pull request #3 from magnetis/chart

Add chart for checkitems