Add modified signal for database.

src/core/Database.cpp

@@ -162,6 +162,7 @@ void Database::setKey(const CompositeKey& key, const QByteArray& transformSeed)
 {
     m_transformSeed = transformSeed;
     m_transformedMasterKey = key.transform(transformSeed, transformRounds());
+    Q_EMIT modified();
 }
 
 void Database::setKey(const CompositeKey& key)

src/core/Database.h

@@ -88,6 +88,7 @@ Q_SIGNALS:
     void groupAdded();
     void groupAboutToRemove(Group* group);
     void groupRemoved();
+    void modified();
 
 private:
     Entry* recFindEntry(const Uuid& uuid, Group* group);