Return instead of closing dialog, if remote form's response is javascript.

We have a event binded on ajax:success for remote forms in dialogs.
If the response type was javascript we closed the current dialog.

This is sometimes not wanted. Instead we just return from the function and let the javascript handle the closing of the dialog.
Always enable buttons of remote forms after ajax response.

If a remote form was submitted, the returning function had to handle the re-enabling of the submit button.
This was not visible because at normal cases the content of the form was replaced from the ajax response.
But sometimes this is not happening and the button had to be re-enabled manually.

Bonus: This also includes a fix for buttons with icons, that loses it's icon after getting disabled.
Fixes ajax request permission error handling.

- Return a text body instead of rendering the action
- Show a growl warning if permission is denied on confirm delete dialogs.
Adds a feature for managing the page's legacy urls.

Every time a user renames the url of a page, a legacy page urls gets created. These urls where hidden to the user. Now the user is able to edit them and even add new ones, what adds some nice SEO related advantages.
Merge pull request #525 from magiclabs/legacy-page-urls-management

Adds a feature for managing the page's legacy urls