Allow programs running in kitty to read/write from the clipboard

By default only writing is allowed. There is a config option to enable
reading, if needed.

kitty/screen.c

@@ -1194,6 +1194,11 @@ set_dynamic_color(Screen *self, unsigned int code, PyObject *color) {
     else { CALLBACK("set_dynamic_color", "IO", code, color); }
 }
 
+void
+clipboard_control(Screen *self, PyObject *data) {
+    CALLBACK("clipboard_control", "O", data);
+}
+
 void
 set_color_table_color(Screen *self, unsigned int code, PyObject *color) {
     if (color == NULL) { CALLBACK("set_color_table_color", "Is", code, ""); }