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/Entry.h

@@ -195,6 +195,7 @@ public:
     Entry* clone(CloneFlags flags) const;
     void copyDataFrom(const Entry* other);
     QString maskPasswordPlaceholders(const QString& str) const;
+    Entry* resolveReference(const QString& str) const;
     QString resolveMultiplePlaceholders(const QString& str) const;
     QString resolvePlaceholder(const QString& str) const;
     QString resolveUrlPlaceholder(const QString& str, PlaceholderType placeholderType) const;