Merge pull request #433 from sharelatex/pr-review-logo-retina

Add retina icon for review features.

services/web/public/stylesheets/app/editor/review-panel.less

@@ -762,6 +762,10 @@
 	.toolbar .btn-full-height:active & {
 		background-position-y: -60px;
 	}
+	
+	@media (min-device-pixel-ratio: 1.5), (min-resolution: 144dpi) {
+		background-image: url('/img/review-icon-sprite@2x.png');
+	}
 }
 
 .resolved-comments-toggle {