add clear_children function for widget

src/Widget.cpp

@@ -106,6 +106,11 @@ void Widget::remove_child(std::shared_ptr<Widget> child) {
     reflow();
 }
 
+void Widget::clear_children() {
+    m_children.clear();
+    reflow();
+}
+
 void Widget::repaint() {
     if (m_window)
         m_window->repaint(this);

src/Widget.hpp

@@ -55,6 +55,7 @@ public:
     std::vector<std::shared_ptr<Widget>> &children() { return m_children; }
     bool add_child(std::shared_ptr<Widget> child);
     void remove_child(std::shared_ptr<Widget> child);
+    void clear_children();
 
     Box &rect() { return m_rect; }
     void set_rect(Box rect) { m_rect = rect; reflow(); }