React Tag Selector polish, i18n and tests

- Added icon-button UI code for the menubutton
- Upgrade to React 16 to allow non-standard attrs, such as `tooltiptext`
to support XUL tooltips
- Add i18n support for React UI elements
- Update tests for reactified tag selector

scripts/watch.js

@@ -34,6 +34,7 @@ const source = [
 const symlinks = symlinkFiles
 				.concat(dirs.map(d => `${d}/**`))
 				.concat([`!${formatDirsForMatcher(dirs)}/**/*.js`])
+				.concat([`!${formatDirsForMatcher(dirs)}/**/*.jsx`])
 				.concat([`!${formatDirsForMatcher(copyDirs)}/**`]);
 
 var signatures;