fix: window title not working on certain WMs

not all WMs support `_NET_WM_NAME` and `_NET_WM_ICON_NAME`
this patch sets `WM_NAME` and `WM_ICON_NAME` inside win_set_title()

Closes: https://github.com/nsxiv/nsxiv/issues/233

nsxiv.h

@@ -381,6 +381,8 @@ enum {
 	ATOM__NET_WM_PID,
 	ATOM__NET_WM_STATE_FULLSCREEN,
 	ATOM_UTF8_STRING,
+	ATOM_WM_NAME,
+	ATOM_WM_ICON_NAME,
 	ATOM_COUNT
 };