webadmin,userportal: Dialog style improvements

This patch improves SimpleDialogPanel widget styles:

1. Generic 'info' icon (shown in the top-left corner)
   removed from dialog header area. Custom dialog icons
   ('error', 'guide-me', etc.) are still supported.

2. Context-sensitive 'help' button (blue icon) moved
   right next to dialog title.

Change-Id: Ifefd84f52fffe8c408d1d2399609fafea66e1862
Signed-off-by: Vojtech Szocs <vszocs@redhat.com>