implemented average active displays per country for last 12 months

- upgraded angular to 1.3 beta to gain access to single bindings to improve table rendering performance
- merged the view and directives for active displays per company and per country to reduce code duplication (will do later in separate PR for other metrics)
- added getDisplaysPerCountry to big query service (with unit tests)
- changed tableHelpersService.orderBy to work for both stat tables
- fixed bower install issue
note: active displays per company has a growth column now with is not connected to service, this is part of the next task

pr is hosted at http://dashboard.risevision.com:8000
trello card : [active displays by country](https://trello.com/c/0OYfdlo1/61-active-displays-by-country)
related proxy PR: https://github.com/Rise-Vision/Dashboard-proxy/pull/35