reverted change in commit 01921e

• it broke the hover states of buttons within the dialog (f.e. newsletter test)
• ui-dialog-content is added again but the rule is overwritten for states within tables within dialog, so the hover state of table rows is correct.
note: I'm not sure this is the right thing to do. It works. But the whole admin css should be eventually evaluated and refactored. I think it could be a lot leaner and cleaner...