Normalize project slugs before querying for them

Summary:
Fixes T5728. In particular:

  - `/tag/XYZ/` now works as an alias for `/tag/xyz/`.
  - `arc todo --project ASDF` now works as an alias for `arc todo --project asdf`.

Test Plan: Called `project.query` and visited `/tag/LBHABLHBH/`.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: aklapper, epriestley

Maniphest Tasks: T5728

Differential Revision: https://secure.phabricator.com/D10144