Output comma when creating date string

Signed-off-by: Olivier Mehani <shtrom@ssji.net>
Ddd dd mm date format

Signed-off-by: Olivier Mehani <shtrom@ssji.net>
Honour clock_is_24h_style()

Also, don't draw empty circles if not needed in double buffer.

Signed-off-by: Olivier Mehani <shtrom@ssji.net>