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/core/Group.h

@@ -74,6 +74,7 @@ public:
     const QList<Group*>& children() const;
     QList<Entry*> entries();
     const QList<Entry*>& entries() const;
+    QList<Entry*> entriesRecursive(bool includeHistoryItems = false);
 
 Q_SIGNALS:
     void dataChanged(Group* group);