added open issue count to github stats table

extended sum filter to only include ints

note: not all repositories have issues enabled, where this occurs, a '-' appears under its open issues to differentiate it from repositories with no open issues. 
![screen shot 2014-07-22 at 5 32 15 pm](https://cloud.githubusercontent.com/assets/3188890/3665617/b39c10ca-11e7-11e4-9df7-4c3992409439.png)


trello: https://trello.com/c/tVZSJiAN (only half of card)
PR hosted at : http://dashboard.risevision.com:8000
relates to: https://github.com/Rise-Vision/Dashboard-proxy/pull/18
could @ByronDarlison @tejohnso @alexey-rise review?