charts for dashboard

  [PT 49574083] interview chart
  [PT 49574095] offer chart
[PT 49430765] generalized solution for data storage layer

    stores both photos and resumes
Merge pull request #153 from Chunjie/master

charts for dashboard
Merge branch 'commonstore'

Conflicts:
	app/controllers/dashboard_controller.rb
	app/models/interview.rb
	app/views/dashboard/_offers_chart.html.slim