Made owncloud submit button more straightforward

As octogen pointed out on irc that's easy to miss that it's necessary
to click the submit button (and not just tick/untick the checkbox)

plinth/modules/owncloud/templates/owncloud.html

@@ -33,7 +33,7 @@
       ownCloud.</p>
 
     {{ form|bootstrap }}
-    <input type="submit" class="btn btn-primary btn-md" value="Update setup"/>
+    <input type="submit" class="btn btn-primary btn-md" value="Apply changes"/>
 
   </form>