lib: add Problem Format API

Related to #303

Signed-off-by: Jakub Filak <jfilak@redhat.com>
bugzilla: port to Proble Format API

Related to #303

Signed-off-by: Jakub Filak <jfilak@redhat.com>
spec: reflect changes due to Problem Report API

Related to #303

Signed-off-by: Jakub Filak <jfilak@redhat.com>