doc: Adding best practises for crypto.pbkdf2
Added some information around usages of how to use iterations, how to choose decent salts and updating the example to have a significant work factor and to use sha512.
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Added some information around usages of how to use iterations, how to choose decent salts and updating the example to have a significant work factor and to use sha512.