Use .png suffix for image URLs

templates/image_detail.html

@@ -8,7 +8,7 @@
         <h2 class="title">{{.Image.Title}}</h2>
     {{end}}
         <a class="image" href="/{{.Image.Id}}">
-            <img src="/{{.Image.Id}}">
+            <img src="/{{.Image.Id}}.png">
         </a>
     {{if .IsMine}}
         <p class="description fake-input" contenteditable="true" placeholder="Description"

templates/image_list.html

@@ -4,7 +4,7 @@
 {{range .Images}}
     <a class="image" href="/i/{{.Id}}">
         <div class="image-container">
-            <img src="/{{.Id}}t">
+            <img src="/{{.Id}}t.png">
         </div>
         <div class="info">
             <p>{{.OriginalName}}</p>