Prevent normal user deleting or modifying too much.

Allow normal user to export board.

Thanks to Samunosuke, pgh2357 and xet7 !

Related #3377

client/components/cards/subtasks.jade

@@ -2,10 +2,10 @@ template(name="subtasks")
   h3.card-details-item-title
     i.fa.fa-sitemap
     | {{_ 'subtasks'}}
-  if toggleDeleteDialog.get
-    .board-overlay#card-details-overlay
-    +subtaskDeleteDialog(subtask = subtaskToDelete)
-
+  if currentUser.isBoardAdmin
+    if toggleDeleteDialog.get
+      .board-overlay#card-details-overlay
+      +subtaskDeleteDialog(subtask = subtaskToDelete)
 
   .card-subtasks-items
     each subtask in currentCard.subtasks
@@ -28,7 +28,8 @@ template(name="subtaskDetail")
         span
         a.js-view-subtask(title="{{ subtask.title }}") {{_ "view-it"}}
         if canModifyCard
-          a.js-delete-subtask.toggle-delete-subtask-dialog {{_ "delete"}}...
+          if currentUser.isBoardAdmin
+            a.js-delete-subtask.toggle-delete-subtask-dialog {{_ "delete"}}...
 
         if canModifyCard
           h2.title.js-open-inlined-form.is-editable
@@ -68,7 +69,8 @@ template(name="editSubtaskItemForm")
     a.fa.fa-times-thin.js-close-inlined-form
     span(title=createdAt) {{ moment createdAt }}
     if canModifyCard
-      a.js-delete-subtask-item {{_ "delete"}}...
+      if currentUser.isBoardAdmin
+        a.js-delete-subtask-item {{_ "delete"}}...
 
 template(name="subtasksItems")
   .subtasks-items.js-subtasks-items