Don't connect more slots to EditProfileDialog::accepted() signal

This is similar to commit c413d543, EditProfileDialog's base class
(KPageDialog) already connects OK button clicked signal to accepted() signal;
creating another connection to accepted() in SessionController (which
creates the EditProfileDialog object), means the code will be run twice, not
ideal. Instead put the logic in EditProfileDialog::save() which is called by
the EditProfileDialog::accept() slot.

The same goes when ProfileSettings creates an EditProfileDialog.