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/ReactorSelectExample.js

@@ -1,8 +1,6 @@
 /**
  * @provides phabricator-uiexample-reactor-select
  * @requires javelin-install
- *           javelin-view
- *           javelin-util
  *           javelin-dom
  *           javelin-reactor-dom
  */
@@ -14,7 +12,7 @@ JX.install('ReactorSelectExample', {
       var select = JX.$N('select', {}, [
         JX.$N('option', { value: 'goat' }, 'Goat'),
         JX.$N('option', { value: 'bat' }, 'Bat'),
-        JX.$N('option', { value: 'duck' }, 'Duck'),
+        JX.$N('option', { value: 'duck' }, 'Duck')
       ]);
 
       return [select, JX.RDOM.$DT(JX.RDOM.select(select))];