Make contextual matching of project monograms more liberal

Summary:
We currently share the same regexp between PHID matching (usually unambiguous) and remarkup matching (often ambiguous).

This means that some project monograms which should work fine don't work properly in some contexts. Improve these behaviors.

For example:

  - `#domain.com`
    - Previously did not work at all.
    - Now works in unambiguous cases, and in remarkup.
  - `#1`
    - Previously did not work at all.
    - Now works in unambiguous cases.
  - `#dot.`
    - Previously did not work at all.
    - Now works in unambiguous cases.

Test Plan:
  - Created projects `domain.com`, `1`, etc.
  - Used jump nav to match them unambiguously, everything worked.
  - Used remarkup preview to match them ambiguously, the reasonable ones worked.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8703