[bug 871567] Code review: front-end code for new metrics on dashboard

This is a first pass at the front-end code for adding new metrics to the dashboard. Please review and provide feedback. I'll then make changes and resubmit this pull request.

Notes
* 'Overdue' and 'empty' icons in the Reports Completed columns need to be added
* Arrow icon that reveals event details doesn't toggle properly
* Event attendance modal will change from a table to a chart once a chart library is selected