Print time point for solar elevation events

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Display previous/next sunset/sunrise and past/future twilight start/end in redshift-gtk

Signed-off-by: Mattias Andrée <maandree@operamail.com>
Merge branch print-twilight into ma and resolve merge conflicts

Signed-off-by: Mattias Andrée <maandree@operamail.com>