gui: Add wallet name to address book page

Extend addresstablemodel to return the display name from the wallet and
set it to the addressbookpage window title when its  model is set.

src/qt/addresstablemodel.h

@@ -87,6 +87,8 @@ public:
 
     OutputType GetDefaultAddressType() const;
 
+    QString GetWalletDisplayName() const;
+
 private:
     WalletModel* const walletModel;
     AddressTablePriv *priv = nullptr;