[Sprint/HipsterHedgehog] client metadata and code refactor

• client metadata added to views, votes
• methods moved from the list stores to the models
• fixed activity editor error
• eslint with flow support added and configured
• added view reporting to discovery and groups feeds (api/v2/analytics/views/)
• added a debounce of 300ms in views reporting
• added error messages to activity actions
• fixed discovery gif optimization (when the image moves out of the screen)

closes #994 (closed) closes #993 (closed) closes #1000 (closed) closes #1002 (closed) closes #1003 (closed) closes #999 (closed) closes #953 (closed) closes #952 (closed) closes #997 (closed)