Implements KDBX4 format with Argon2 KDF

* Adds KDBX4 reader/writer interfaces
* Adds KDBX4 XML reader/write interfaces
* Implements test cases for KDBX4
* Fully compatible with KeePass2
* Corrects minor issues with Argon2 KDF

src/core/Database.cpp

@@ -494,6 +494,14 @@ void Database::setKdf(QSharedPointer<Kdf> kdf)
     m_data.kdf = std::move(kdf);
 }
 
+void Database::setPublicCustomData(QByteArray data) {
+    m_data.publicCustomData = data;
+}
+
+QByteArray Database::publicCustomData() const {
+    return m_data.publicCustomData;
+}
+
 bool Database::changeKdf(QSharedPointer<Kdf> kdf)
 {
     kdf->randomizeSeed();