Merge #85: Remove unused "What's This" button in dialogs on Windows OS

ac7ccd6 scripted-diff: Remove unused "What's This" button in dialogs on Windows (Hennadii Stepanov)
b695148 qt: Add flags to prevent a "What's This" button on Windows OS (Hennadii Stepanov)

Pull request description:

  Fix #74.

  From [Qt docs](https://doc.qt.io/qt-5/qdialog.html#QDialog):
  > The widget flags _f_ are passed on to the `QWidget` constructor. If, for example, you don't want a **What's This** button in the title bar of the dialog, pass `Qt::WindowTitleHint | Qt::WindowSystemMenuHint` in _f_.

  Screenshot on Windows 10 (2004):
  - master (3ba25e3)
  ![Screenshot from 2020-09-07 16-55-42](https://user-images.githubusercontent.com/32963518/92402384-20dc6a00-f138-11ea-9dcb-3e0f6373ff22.png)

  - this PR (e322fe7)
  ![Screenshot from 2020-09-07 18-31-16](https://user-images.githubusercontent.com/32963518/92402509-5aad7080-f138-11ea-8b63-9bbbf8b9b9e1.png)

ACKs for top commit:
  Bosch-0:
    tACK ac7ccd6 Tested on Windows 10.0.18363 Build 18363.
  promag:
    Code review ACK ac7ccd6 but with some suggestions.
  jonasschnelli:
    utACK ac7ccd6

Tree-SHA512: f6750a17b7203106cb4db5870becba1cef6a505d4edcc710ba131338bd3aae051510627e62c9bcb8345a7f497c614709e11aeb8f6ae3ea85967bbce2a8c69e64

Author: jonasschnelli

src/qt/addressbookpage.cpp

@@ -56,7 +56,7 @@ class AddressBookSortFilterProxyModel final : public QSortFilterProxyModel
 };
 
 AddressBookPage::AddressBookPage(const PlatformStyle *platformStyle, Mode _mode, Tabs _tab, QWidget *parent) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::AddressBookPage),
     model(nullptr),
     mode(_mode),

src/qt/askpassphrasedialog.cpp

@@ -20,7 +20,7 @@
 #include <QPushButton>
 
 AskPassphraseDialog::AskPassphraseDialog(Mode _mode, QWidget *parent, SecureString* passphrase_out) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::AskPassphraseDialog),
     mode(_mode),
     model(nullptr),

src/qt/coincontroldialog.cpp

@@ -42,7 +42,7 @@ bool CCoinControlWidgetItem::operator<(const QTreeWidgetItem &other) const {
 }
 
 CoinControlDialog::CoinControlDialog(CCoinControl& coin_control, WalletModel* _model, const PlatformStyle *_platformStyle, QWidget *parent) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::CoinControlDialog),
     m_coin_control(coin_control),
     model(_model),

src/qt/createwalletdialog.cpp

@@ -9,10 +9,12 @@
 #include <qt/createwalletdialog.h>
 #include <qt/forms/ui_createwalletdialog.h>
 
+#include <qt/guiutil.h>
+
 #include <QPushButton>
 
 CreateWalletDialog::CreateWalletDialog(QWidget* parent) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::CreateWalletDialog)
 {
     ui->setupUi(this);

src/qt/editaddressdialog.cpp

@@ -13,7 +13,7 @@
 
 
 EditAddressDialog::EditAddressDialog(Mode _mode, QWidget *parent) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::EditAddressDialog),
     mapper(nullptr),
     mode(_mode),

src/qt/guiutil.h

@@ -45,6 +45,9 @@ QT_END_NAMESPACE
  */
 namespace GUIUtil
 {
+    // Use this flags to prevent a "What's This" button in the title bar of the dialog on Windows.
+    constexpr auto dialog_flags = Qt::WindowTitleHint | Qt::WindowSystemMenuHint | Qt::WindowCloseButtonHint;
+
     // Create human-readable string from date
     QString dateTimeStr(const QDateTime &datetime);
     QString dateTimeStr(qint64 nTime);

src/qt/intro.cpp

@@ -119,7 +119,7 @@ int GetPruneTargetGB()
 } // namespace
 
 Intro::Intro(QWidget *parent, int64_t blockchain_size_gb, int64_t chain_state_size_gb) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::Intro),
     thread(nullptr),
     signalled(false),

src/qt/openuridialog.cpp

@@ -11,7 +11,7 @@
 #include <QUrl>
 
 OpenURIDialog::OpenURIDialog(QWidget *parent) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::OpenURIDialog)
 {
     ui->setupUi(this);

src/qt/optionsdialog.cpp

@@ -29,7 +29,7 @@
 #include <QTimer>
 
 OptionsDialog::OptionsDialog(QWidget *parent, bool enableWallet) :
-    QDialog(parent),
+    QDialog(parent, GUIUtil::dialog_flags),
     ui(new Ui::OptionsDialog),
     model(nullptr),
     mapper(nullptr)

src/qt/psbtoperationsdialog.cpp

@@ -19,7 +19,7 @@
 
 
 PSBTOperationsDialog::PSBTOperationsDialog(
-    QWidget* parent, WalletModel* wallet_model, ClientModel* client_model) : QDialog(parent),
+    QWidget* parent, WalletModel* wallet_model, ClientModel* client_model) : QDialog(parent, GUIUtil::dialog_flags),
                                                                              m_ui(new Ui::PSBTOperationsDialog),
                                                                              m_wallet_model(wallet_model),
                                                                              m_client_model(client_model)