Factor out presenation-related code from decode_time.[ch]:
- move display_time_file() to dcf77pi-analyze.c
- move display_time_gui() and draw_time_window() to dcf77pi.c
- Move declaration from decode_win from decode_time.h to dcf77pi.c and
  remove dependency on ncurses.h
- Move declaration from wday[] from decode_time.c to decode_time.h
- Change return value of decode_time to also include
  announcements (DST, leap second) and make it uint32_t.
  Change ANN_CHDST and ANN_LEAP to not collide with DT_ values.

While here, fix a '&&' which should have been a '&' in display_time_gui()
(DST announcement)