Add a workaround for a Babel + browserify-ngannotate interaction issue.

Babel inserts helper code before the first non-comment statement from the original
source, breaking the `@ngInject` annotation.

src/sidebar/view-filter.js

 'use strict';
 
+// Prevent Babel inserting helper code after `@ngInject` comment below which
+// breaks browserify-ngannotate.
+var unused; // eslint-disable-line
+
 // @ngInject
 function viewFilter(unicode) {
   /**