Set card attachment as background image. In Progress.

Thanks to xet7 !

Related #486

client/components/cards/attachments.jade

@@ -81,6 +81,13 @@ template(name="attachmentActionsPopup")
             | {{_ 'remove-cover'}}
           else
             | {{_ 'add-cover'}}
+      if isImage
+        a(class="{{#if isBackgroundImage}}js-remove-background-image{{else}}js-add-background-image{{/if}}")
+          i.fa.fa-picture-o
+          if isBackgroundImage
+            | {{_ 'remove-background-image'}}
+          else
+            | {{_ 'add-background-image'}}
       if currentUser.isBoardAdmin
         a.js-rename
           i.fa.fa-pencil-square-o

imports/i18n/data/en.i18n.json

@@ -140,6 +140,8 @@
   "board-change-color": "Change color",
   "board-change-background-image": "Change Background Image",
   "board-background-image-url": "Background Image URL",
+  "add-background-image": "Add Background Image",
+  "remove-background-image": "Remove Background Image",
   "show-at-all-boards-page" : "Show at All Boards page",
   "board-info-on-my-boards" : "All Boards Settings",
   "boardInfoOnMyBoardsPopup-title" : "All Boards Settings",