Fix for issue 4157 (Control Panel does not display Mac OS menu bar in Browse Entries dialog)

Since all the dialogs (except for the main one) in the control panel are JDialog objects, they appear as secondary dialogs and the Mac OS menu bar do not appear on the top of the screen.

Some issues have been also reported because of this in Windows 2008, where the secondary dialogs are not resizable.  The solution for this is to use JFrame instead of JDialog for the windows that are displayed when the user clicks on the left side actions (Import LDIF, Manage Entries, etc.).