shell/aliases: add a function to retrieve HTTPS certificates from websites

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
Add check_certificate.py script to check certificates validity

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>
shell and profile: make files compatible with dash

Signed-off-by: Nicolas Iooss <nicolas.iooss_git@polytechnique.org>