(sieve-sasl-auth): Quote optional initial SASL

(sieve-sasl-auth): Quote optional initial SASL
token.
(require): Use SASL, not RFC2104/MD5.
(sieve-manage-authenticators):
(sieve-manage-authenticator-alist): Add some SASL mechs.
(sieve-sasl-auth): New function.
(sieve-manage-cram-md5-auth):
(sieve-manage-plain-auth): Rewrite using SASL library.
(sieve-manage-digest-md5-p, sieve-manage-digest-md5-auth)
(sieve-manage-scram-md5-p, sieve-manage-scram-md5-auth)
(sieve-manage-ntlm-p, sieve-manage-ntlm-auth)
(sieve-manage-login-p, sieve-manage-login-auth): Add wrappers.