Simplify usage of AbstractDialog.getTranslatedException

Hi,

In order to provide specific or localized messages, a class that extends AbstractDialog must encode the message key into the thrown exception and also add the localized message to the hippo-cms-api package where AbstractDialog exists.

Because these two classes can be in totally different (see CMS7-6409) packages, it is a non-obvious design.

AbstractDialog should be simplified to move the localization closer to the extending class.