renamed unnotify functions for consistency

No functional changes in this patch.

The functions

  screen_nowindowinfo
  screen_unnotify

are now called

  screen_unnotify_infowin
  screen_unnotify_notifywin

This is consistent with the already-existing pair

  screen_update_infowin
  screen_update_notifywin
reduced boilerplate in get_notifywin/get_infowin

This is minor refactoring for consistency. No functional changes
Renamed do_get_notifywin -> do_get_popup_win

This indicates that this function is used for both notify and info windows
Added transient workspace indicator in corner

When a new workspace (or screen) is selected, an indicator can pop up stating
the name of this workspace. The indicator goes away after a predetermined
timeout. The duration of the indicator is set in the configuration file. By
default this indicator is disabled entirely