SqliteTableModel: Don't show binary data in table widgets

Don't show BLOBs as binary data in table widgets, instead put a "BLOB"
text in that cell.

Also make BLOBs not editable unless you use the edit dialog.

src/sqlitetablemodel.h

@@ -35,6 +35,8 @@ public:
 
     bool valid() const { return m_valid; }
 
+    bool isBinary(const QModelIndex& index) const;
+
     typedef QList<QByteArray> QByteArrayList;
 
 signals: