Support KeePass format 3.00 (used by KeePass2 >= 2.15).

Closes #6

Attachments are now stored in a pool under Metadata instead of in entries.
The protected flag of attachments isn't supported anymore.
New metadata attributes: color, historyMaxItems and historyMaxSize.
Dropped metadata attribute: autoEnableVisualHiding.

src/format/KeePass2XmlWriter.h

@@ -43,10 +43,13 @@ public:
     QString errorString();
 
 private:
+    void generateIdMap();
+
     void writeMetadata();
     void writeMemoryProtection();
     void writeCustomIcons();
     void writeIcon(const Uuid& uuid, const QImage& icon);
+    void writeBinaries();
     void writeCustomData();
     void writeCustomDataItem(const QString& key, const QString& value);
     void writeRoot();
@@ -75,6 +78,7 @@ private:
     Database* m_db;
     Metadata* m_meta;
     KeePass2RandomStream* m_randomStream;
+    QHash<QByteArray, int> m_idMap;
 };
 
 #endif // KEEPASSX_KEEPASS2XMLWRITER_H