Move discussions and homepage to feature branch, bring links back into focus

## Overview

Moves the discussions feature to a feature branch and reverting master back. Since the home page is discussion focused, this also reverts the home page. 

## Motivation
User activity has dived since this change (even with core users) so it seems like a good idea to take this feature off master and work on it a bit before re-introducing it. See [pullup.io/chat](http://pullup.io/chat) for discussion.

## Notes
This keeps the [commits](https://github.com/larvalabs/pullup/pull/357) by @Caraheacock, which were the only commits after the discussion branch.