Simplify Diffusion main view

Summary:
Currently, Diffusion has very complex views. After three years I'm not really used to them and rarely use many of these options.

Simplify the browse and history views:

  - Put the browse view on top.
  - Move dates to the right.
  - Remove "History" and "Edit" links from the browse view. You can access these actions by clicking the file/path.
  - Remove "Browse" link from the history view. You can access this action by clicking the commit.
  - Remove "Change Type", which is essentially never useful, from the history view.
  - Add some tweaks for mobile.

Test Plan: {F153931}

Reviewers: btrahan, chad

Reviewed By: chad

Subscribers: epriestley, zeeg

Differential Revision: https://secure.phabricator.com/D9085