Add the possibility to edit Jira error pages

After JIRA 6.1, error pages (500, 400 and so on) use a soy template to create themselves. This disables the possibility to easily edit these pages so that they just add the information needed in a secure manner.

So my request is that JIRA adds the possibility to edit these pages to not show the stacktrace. JUST inform the user that an error has happened and that he/she needs to grab assistance from the admin.

 Similar to JRASERVER-38101, in some cases, no error is visible in the GUI but still can be captured by the browser's F12 tools. The implementation of this feature should take this into account as well.