Use cursor: pointer on image attachments

Because clicking on an image now opens it in a new browser window.

// FREEBIE

stylesheets/_conversation.scss

@@ -358,6 +358,10 @@
     video {
       background: black;
     }
+
+    img {
+      cursor: pointer;
+    }
   }
 
   .outgoing .avatar {

stylesheets/manifest.css

@@ -797,6 +797,9 @@ input.search {
   .message-detail .attachments video,
   .message-list .attachments video {
     background: black; }
+  .message-detail .attachments img,
+  .message-list .attachments img {
+    cursor: pointer; }
   .message-detail .outgoing .avatar,
   .message-list .outgoing .avatar {
     display: none; }