qt: Plug many memory leaks

None of these are very serious, and are leaks in objects that are
created at most one time.

In most cases this means properly using the QObject parent hierarchy,
except for BanTablePriv/PeerTablePriv which are not QObject,
so use a std::unique_ptr instead.

src/qt/peertablemodel.cpp

@@ -114,12 +114,12 @@ PeerTableModel::PeerTableModel(ClientModel *parent) :
     timer(0)
 {
     columns << tr("NodeId") << tr("Node/Service") << tr("User Agent") << tr("Ping");
-    priv = new PeerTablePriv();
+    priv.reset(new PeerTablePriv());
     // default to unsorted
     priv->sortColumn = -1;
 
     // set up timer for auto refresh
-    timer = new QTimer();
+    timer = new QTimer(this);
     connect(timer, SIGNAL(timeout()), SLOT(refresh()));
     timer->setInterval(MODEL_UPDATE_DELAY);
 
@@ -127,6 +127,11 @@ PeerTableModel::PeerTableModel(ClientModel *parent) :
     refresh();
 }
 
+PeerTableModel::~PeerTableModel()
+{
+    // Intentionally left empty
+}
+
 void PeerTableModel::startAutoRefresh()
 {
     timer->start();