Replace `/conpherence/N/` with `/conpherence/view/N/`.

Summary:
  - Move `/N/` to `/thread/N/`.
  - Move `/view/N/` to `/N`/.
  - This makes the mobile "Conpherence -> click thread -> see thread" workflow work correctly. This also makes permalinks work correctly on mobile.

Ref T2421.

Test Plan: Clicked flows on desktop, mobile.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2421

Differential Revision: https://secure.phabricator.com/D5508