MEDIUM: ssl: Add "new+del crl-file" CLI commands

MEDIUM: ssl: Add "new+del crl-file" CLI commands

This patch adds the "new ssl crl-file" and "del ssl crl-file" CLI
commands.
The "new" command can be used to create a new empty CRL file that can be
filled in thanks to a "set ssl crl-file" command. It can then be used in
a new crt-list line.
The newly created CRL file is added to the CA file tree so any call to
"show ssl crl-file" will display its name.
The "del" command allows to delete an unused CRL file. A CRL file will
be considered unused if its list of ckch instances is empty. It does not
work on an uncommitted CRL file transaction created via a "set ssl
crl-file" command call.