Switch to modern method for self-signed cert generation

[MichaIng]

pyOpenSSL discourages itself for that task. Also at least SAN is missing to every allow browser accepting that certificate: https://pypi.org/project/pyOpenSSL/
Strange that in 9/10 guide search results that exact method is still used.

Better go with cryptography: https://gist.github.com/bloodearnest/9017111a313777b9cce5
Official docs: https://cryptography.io/en/latest/x509/tutorial/#creating-a-self-signed-certificate

• Here is the function, called when SSL is enabled but no certificate/key found: https://github.com/HTPC-Manager/HTPC-Manager/blob/master2/htpc/helpers.py#L323
• It imports functions from this library: https://github.com/HTPC-Manager/HTPC-Manager/blob/master2/libs/certgen.py
• Both are basically 13 years old examples from pyOpenSSL: https://github.com/msabramo/pyOpenSSL/blob/master/examples/mk_simple_certs.py, https://github.com/msabramo/pyOpenSSL/blob/master/examples/certgen.py