Filter "javascript:" URIs more aggressively

Summary: Some browsers interpret `javascript\n:` as a Javascript URI. Be significantly more aggressive in normalizing URIs when looking for `javascript:` hrefs.

Test Plan: Added and executed unit tests.

Reviewers: btrahan

Reviewed By: btrahan

Subscribers: epriestley

Differential Revision: https://secure.phabricator.com/D8548