big refactor to use a single feed view

This PR updates the app to use a single feed view on the index route. It fetches the project membership to get the user (project ID is hardcoded) and uses the response to build App.users. Then, the ActivityCollection is fetched and the feed view populated. I created a custom ChangesFormatter since I didn't want to mess w/ Handlebars custom functions.

It doesn't require an app server now, and there's no real routing to speak of.