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/core/Config.cpp

@@ -48,7 +48,16 @@ QString Config::getFileName()
 
 void Config::set(const QString& key, const QVariant& value)
 {
+    if (m_settings->contains(key) && m_settings->value(key) == value) {
+        return;
+    }
+    const bool surpressSignal = !m_settings->contains(key) && m_defaults.value(key) == value;
+
     m_settings->setValue(key, value);
+
+    if (!surpressSignal) {
+        emit changed(key);
+    }
 }
 
 /**