Allow "arc browse" to browse objects

Summary: Ref T5781. This implements `arc browse T234`, for any monogrammed object.

Test Plan:
  - Ran `arc browse T234` outside of a working copy (does not require repository API).
  - Ran `arc browse T234` in a working copy, got task.
  - Ran `arc browse PATH` in a working copy.
  - Ran `arc browse nonpath` with and without `--force`.

Reviewers: csilvers, btrahan

Reviewed By: btrahan

Subscribers: epriestley, spicyj

Maniphest Tasks: T5781

Differential Revision: https://secure.phabricator.com/D10140