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/Tools.cpp

@@ -346,4 +346,31 @@ namespace Tools
         return bSuccess;
     }
 
+
+    Buffer::Buffer()
+        : raw(nullptr)
+        , size(0)
+    {
+
+    }
+
+    Buffer::~Buffer()
+    {
+        clear();
+    }
+
+    void Buffer::clear()
+    {
+        if(size > 0){
+            free(raw);
+        }
+        raw = nullptr; size = 0;
+    }
+
+    QByteArray Buffer::content() const
+    {
+        return QByteArray(reinterpret_cast<char*>(raw), size );
+    }
+
+
 } // namespace Tools