...entering the pwd for the certificate store
Also Move CertificateStoreImpl to PopplerCertificateStore, since
PopplerCertificateStore was declared but never defined and use it
in CertificateTools to get the certificate list instead of calling
the poppler classes directly
* Don't make WidgetAnnotation know about signatures stuff, widget
annotations are for multiple things
* Don't create an "empty" widget annotation and then call sign on it
(which is wrong because widget annotations can be multiple things),
just say sign the document with this data (cert, l&f, etc)
* Remove the "management" functionality from CertificateTools it was
only visual, i.e. it didn't really add/remove certificates
* Ask for the NSS password (if needed)