Pause dunst while the screen is locked; add notification history keys

screen-lock holds notifications until unlock, and M-S-l now goes through
loginctl lock-session so it uses the same locker. M-S-n pops dunst history,
M-C-n closes all notifications.

.config/xmonad/xmonad.hs

@@ -118,7 +118,9 @@ myConfig =
       logHook = myLogHook
     }
     `additionalKeysP` [ ("M-b", sendMessage ToggleStruts),
-                        ("M-S-l", spawn "slock"),
+                        ("M-S-l", spawn "loginctl lock-session"),
+                        ("M-S-n", spawn "dunstctl history-pop"),
+                        ("M-C-n", spawn "dunstctl close-all"),
                         ("<Print>", unGrab *> spawn ("scrot " ++ myScreenshotDir ++ myScreenshotName)),
                         ("S-<Print>", unGrab *> spawn ("scrot -s " ++ myScreenshotDir ++ myScreenshotName)),
                         ("M-S-<Print>", unGrab *> spawn ("scrot -u " ++ myScreenshotDir ++ myScreenshotName)),