Change gui_always_on_top to true, by default (fixes #1351)

Set the GUI to be always on top by default.
This should help with cases where we are in Full screen mode, and sometimes the GUI opens behind the emulation screen.

src/osdep/amiberry.cpp

@@ -2155,7 +2155,7 @@ void target_default_options(struct uae_prefs* p, int type)
 		//p->notaskbarbutton = false;
 		//p->nonotificationicon = false;
 		p->main_alwaysontop = false;
-		p->gui_alwaysontop = false;
+		p->gui_alwaysontop = true;
 		//p->guikey = -1;
 		p->automount_removable = false;
 		//p->automount_drives = 0;