Don't use a new window for adding and editing a contact

[Martin Weißhaupt]

At the moment Dexter opens a new window when adding or editing a contact.

I think it would be better for usability especialy on netbooks if dexter wouldn't open a new window for this action but use the already displayed area to render the input fields. The addressbook of Mac OSX does this and the project contacts from http://www.pimlico-project.org/ does this too.