Add sharing of groups between databases

* Add source folder keeshare for sharing with corresponding define WITH_XC_KEESHARE
* Move common crypto parts to src/crypto/ssh
* Extended OpenSSHKey
* Move filewatching to own file (currently in two related classes DelayedFileWatcher and BulkFileWatcher)
* Small improvements for style and code in several classes
* Sharing is secured using RSA-Keys which are generated on demand
* Publisher signs the container using their private key
* Client can verify the signed container and choose to decline an import,
import only once or trust the publisher and automatically import all
data of this source henceforth
* Integration of settings into Group-Settings, Database-Settings and Application-Settings
* Introduced dependency QuaZip as dependency to allow combined export of
key container and the (custom format) certificate

src/format/KdbxXmlWriter.cpp

@@ -34,7 +34,7 @@ KdbxXmlWriter::KdbxXmlWriter(quint32 version)
 }
 
 void KdbxXmlWriter::writeDatabase(QIODevice* device,
-                                  Database* db,
+                                  const Database* db,
                                   KeePass2RandomStream* randomStream,
                                   const QByteArray& headerHash)
 {