WIP: Moved sources int src/, separated most of the source code from Perl.

The XS was left only for the unit / integration tests, and it links
libslic3r only. No wxWidgets are allowed to be used from Perl starting
from now.

src/slic3r/GUI/ProgressStatusBar.hpp

@@ -0,0 +1,68 @@
+#ifndef PROGRESSSTATUSBAR_HPP
+#define PROGRESSSTATUSBAR_HPP
+
+#include <memory>
+#include <functional>
+
+#include "callback.hpp"
+
+class wxTimer;
+class wxGauge;
+class wxButton;
+class wxTimerEvent;
+class wxStatusBar;
+class wxWindow;
+class wxFrame;
+class wxString;
+
+namespace Slic3r {
+
+/**
+ * @brief The ProgressStatusBar class is the widgets occupying the lower area
+ * of the Slicer main window. It consists of a message area to the left and a
+ * progress indication area to the right with an optional cancel button.
+ */
+class ProgressStatusBar {
+    wxStatusBar *self;      // we cheat! It should be the base class but: perl!
+    wxTimer *timer_;
+    wxGauge *prog_;
+    wxButton *cancelbutton_;
+public:
+
+    /// Cancel callback function type
+    using CancelFn = std::function<void()>;
+
+    ProgressStatusBar(wxWindow *parent = nullptr, int id = -1);
+    ~ProgressStatusBar();
+
+    int  get_progress() const;
+    void set_progress(int);
+    int  get_range() const;
+    void set_range(int = 100);
+    void show_progress(bool);
+    void start_busy(int = 100);
+    void stop_busy();
+    inline bool is_busy() const { return busy_; }
+    void set_cancel_callback(CancelFn = CancelFn());
+    inline void remove_cancel_callback() { set_cancel_callback(); }
+    void run(int rate);
+    void embed(wxFrame *frame = nullptr);
+    void set_status_text(const wxString& txt);
+
+    // Temporary methods to satisfy Perl side
+    void show_cancel_button();
+    void hide_cancel_button();
+
+    PerlCallback m_perl_cancel_callback;
+private:
+    bool busy_ = false;
+    CancelFn cancel_cb_;
+};
+
+namespace GUI {
+    using Slic3r::ProgressStatusBar;
+}
+
+}
+
+#endif // PROGRESSSTATUSBAR_HPP