add ability to edit messages

dialogs/editmessage.hpp

@@ -0,0 +1,20 @@
+#pragma once
+#include <gtkmm.h>
+#include <string>
+
+class EditMessageDialog : public Gtk::Dialog {
+public:
+    EditMessageDialog(Gtk::Window &parent);
+    std::string GetContent();
+
+protected:
+    Gtk::Box m_layout;
+    Gtk::Button m_ok;
+    Gtk::Button m_cancel;
+    Gtk::ButtonBox m_bbox;
+    Gtk::ScrolledWindow m_scroll;
+    Gtk::TextView m_text;
+
+private:
+    std::string m_content;
+};