New 'default' homepage

Summary: Ref T11132. This is a new default default (no dashboard) homepage. It offers (Diffs) (Tasks) (Repositories) in the main column and (Feed) in the side column. No NUX stuff, No logged out public view (upcoming diff). This should be complete, but unclear how to bucketize Differential.

Test Plan: Test new account's default homepage.

Reviewers: epriestley

Reviewed By: epriestley

Subscribers: Korvin

Maniphest Tasks: T11132

Differential Revision: https://secure.phabricator.com/D16449