Use JsShrink if jsxmin is not available

Summary: If `jsxmin` is not available, use a pure PHP implementation instead (JsShrink).

Test Plan:
  - Ran `arc lint --lintall` on all JS and fixed every relevant warning.
  - Forced minification on and browsed around the site using JS behaviors. Didn't hit anything problematic.

Reviewers: vrana, btrahan

Reviewed By: vrana

CC: aran, Korvin

Differential Revision: https://secure.phabricator.com/D5670

webroot/rsrc/js/application/uiexample/ReactorInputExample.js

@@ -1,9 +1,6 @@
 /**
  * @provides phabricator-uiexample-reactor-input
  * @requires javelin-install
- *           javelin-view
- *           javelin-util
- *           javelin-dom
  *           javelin-reactor-dom
  *           javelin-view-html
  *           javelin-view-interpreter