Introduce FrameworkWidgetFactory

The framework uses a few QWidgets (FrameWidget, TabbarWidget, TabWidget
TitleBarWidget). This factory allows the user to provide his own,
to achieve different appearence.

src/FrameworkWidgetFactory.h

@@ -0,0 +1,53 @@
+/*
+  This file is part of KDDockWidgets.
+
+  Copyright (C) 2019 Klarälvdalens Datakonsult AB, a KDAB Group company, info@kdab.com
+  Author: Sérgio Martins <sergio.martins@kdab.com>
+
+  This program is free software; you can redistribute it and/or modify
+  it under the terms of the GNU General Public License as published by
+  the Free Software Foundation, either version 2 of the License, or
+  (at your option) any later version.
+
+  This program is distributed in the hope that it will be useful,
+  but WITHOUT ANY WARRANTY; without even the implied warranty of
+  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+  GNU General Public License for more details.
+
+  You should have received a copy of the GNU General Public License
+  along with this program.  If not, see <http://www.gnu.org/licenses/>.
+*/
+
+#ifndef KDDOCKWIDGETS_FRAMEWORKWIDGETFACTORY_H
+#define KDDOCKWIDGETS_FRAMEWORKWIDGETFACTORY_H
+
+#include "Frame_p.h"
+#include "TitleBar_p.h"
+#include "TabWidget_p.h"
+
+namespace KDDockWidgets {
+
+class FrameworkWidgetFactory {
+public:
+    virtual ~FrameworkWidgetFactory();
+
+    virtual Frame* createFrame(QWidget *parent = nullptr, Frame::Options = Frame::Option_None) const = 0;
+    virtual TitleBar* createTitleBar(Frame *) const = 0;
+    virtual TitleBar* createTitleBar(FloatingWindow *) const = 0;
+    virtual TabBar* createTabBar(TabWidget *parent = nullptr) const = 0;
+    virtual TabWidget* createTabWidget(QWidget *parent) const = 0;
+};
+
+class DefaultWidgetFactory : public FrameworkWidgetFactory
+{
+public:
+    Frame *createFrame(QWidget *parent, Frame::Options) const override;
+    TitleBar *createTitleBar(Frame *) const override;
+    TitleBar *createTitleBar(FloatingWindow *) const override;
+    TabBar *createTabBar(TabWidget *parent) const override;
+    TabWidget *createTabWidget(QWidget *parent) const override;
+};
+
+}
+
+#endif