provide higher resolution previews on devices that support it

work in progress ...

www/maposmatic/templates/maposmatic/index-parts/carousel.html

@@ -9,13 +9,13 @@
   <!-- Wrapper for slides -->
   <div class="carousel-inner">
     <div class="carousel-item active">
-      <img src="/media/img/preview-1.png" width="100%" alt="plain layout">
+      <img src="/media/img/preview-1.png" srcset="/media/img/preview-1.png, /media/img/preview-1d.png 2x" width="100%" alt="plain layout">
       <div class="carousel-caption">
       	<h3>Plain Layout</h3>
       </div>
     </div>
     <div class="carousel-item">
-      <img src="/media/img/preview-2.png"  width="100%" alt="side index layout">
+      <img src="/media/img/preview-2.png" srcset="/media/img/preview-2.png, /media/img/preview-2d.png 2x" width="100%" alt="plain layout">
       <div class="carousel-caption">
       	<h3>Side Index Layout</h3>
       </div>