Apply all the clang-tidy modernize-* fixes

Pass the shared_ptr by reference, to avoid useless copies

Remove the embedded sha1 code, and use one of botan or gcrypt

This adds a hard dependency on one of Botan or gcrypt. Botan is already a
recommended dependency, and gcrypt is probably packaged almost everywhere,
so this should not be a big deal.

ref #3241

Add some missing includes

Clean a few more things

fix an “unused parameter” warning

Fix some little compilation errors with some configs, from last commit

Support the ident protocol

fix #3211