Add common dialog wxCredentialEntryDialog

Prompting for user name and password is a common task.
At least windows provides these dialogs native but this
is just a generic implementation for now.

include/wx/generic/creddlgg.h

@@ -0,0 +1,55 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/generic/creddlgg.h
+// Purpose:     wxGenericCredentialEntryDialog interface
+// Author:      Tobias Taschner
+// Created:     2018-10-23
+// Copyright:   (c) 2018 wxWidgets development team
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_CREDDLGG_H_BASE
+#define _WX_CREDDLGG_H_BASE
+
+#include "wx/defs.h"
+
+#if wxUSE_CREDENTIALDLG
+
+#include "wx/dialog.h"
+
+class WXDLLIMPEXP_CORE wxGenericCredentialEntryDialog : public wxDialog
+{
+public:
+    wxGenericCredentialEntryDialog();
+
+    wxGenericCredentialEntryDialog(wxWindow* parent, const wxString& message,
+        const wxString& title,
+        const wxString& user = "",
+        const wxString& password = "");
+
+    bool Create(wxWindow* parent, const wxString& message,
+        const wxString& title,
+        const wxString& user = "",
+        const wxString& password = "");
+
+    wxString GetUser() const { return m_userTextCtrl->GetValue(); }
+    void SetUser(const wxString& user) { m_userTextCtrl->SetValue(user); }
+
+    wxString GetPassword() const { return m_passwordTextCtrl->GetValue(); }
+    void SetPassword(const wxString& password)
+        { m_passwordTextCtrl->SetValue(password); }
+
+private:
+    wxTextCtrl* m_userTextCtrl;
+    wxTextCtrl* m_passwordTextCtrl;
+
+    void Init(const wxString& message,
+        const wxString& user,
+        const wxString& password);
+};
+
+// Add this typedef as long as the generic version is the only one available
+typedef wxGenericCredentialEntryDialog wxCredentialEntryDialog;
+
+#endif // wxUSE_CREDENTIALDLG
+
+#endif // _WX_CREDDLGG_H_BASE