Use newer digest algorithms in TLS error dialog

Use newer digest algorithms in TLS error dialog

MD5 has been broken for a long time now and SHA1 has been
deprecated as well. SHA1 is not used when issuing new
publicly trusted certificates since 1 January 2016[1] and
there are more and more effective attacks[2][3] against it,
so display SHA1 fingerprint only for old certificates
to encourage use of safer digests by users.

So, we display SHA-256 and SHA-512 fingerprints instead in
the common case.

[1] https://cabforum.org/wp-content/uploads/CA-Browser-Forum-BR-1.6.5.pdf
[2] https://shattered.io/static/shattered.pdf
[3] https://eprint.iacr.org/2019/459.pdf

Signed-off-by: Martin Sucha <git@mm.ms47.eu>