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/overviewpage.cpp

@@ -25,8 +25,8 @@ class TxViewDelegate : public QAbstractItemDelegate
 {
     Q_OBJECT
 public:
-    TxViewDelegate(const PlatformStyle *_platformStyle):
-        QAbstractItemDelegate(), unit(BitcoinUnits::BTC),
+    TxViewDelegate(const PlatformStyle *_platformStyle, QObject *parent=nullptr):
+        QAbstractItemDelegate(parent), unit(BitcoinUnits::BTC),
         platformStyle(_platformStyle)
     {
 
@@ -119,8 +119,7 @@ OverviewPage::OverviewPage(const PlatformStyle *platformStyle, QWidget *parent)
     currentWatchOnlyBalance(-1),
     currentWatchUnconfBalance(-1),
     currentWatchImmatureBalance(-1),
-    txdelegate(new TxViewDelegate(platformStyle)),
-    filter(0)
+    txdelegate(new TxViewDelegate(platformStyle, this))
 {
     ui->setupUi(this);
 
@@ -220,7 +219,7 @@ void OverviewPage::setWalletModel(WalletModel *model)
     if(model && model->getOptionsModel())
     {
         // Set up transaction list
-        filter = new TransactionFilterProxy();
+        filter.reset(new TransactionFilterProxy());
         filter->setSourceModel(model->getTransactionTableModel());
         filter->setLimit(NUM_ITEMS);
         filter->setDynamicSortFilter(true);
@@ -228,7 +227,7 @@ void OverviewPage::setWalletModel(WalletModel *model)
         filter->setShowInactive(false);
         filter->sort(TransactionTableModel::Date, Qt::DescendingOrder);
 
-        ui->listTransactions->setModel(filter);
+        ui->listTransactions->setModel(filter.get());
         ui->listTransactions->setModelColumn(TransactionTableModel::ToAddress);
 
         // Keep up to date with wallet