Bug 838192 - Add screenshot functionality to the Dashboard

Added screenshot functionality to the Dashboard

Some examples:
http://mozmill-sandbox.blargon7.com/#/l10n/report/2a6536e9db9f5f44ed48c585101c1126
http://mozmill-sandbox.blargon7.com/#/functional/report/2a6536e9db9f5f44ed48c585101cc554