Increase dh primes to 4096 bits and load ssl-dhparams.pem and options-ssl-nginx.conf configs

[stcz]

Currently, the options-ssl-nginx.conf file is not included in the nginx configuration.

This will add it.

Further increase the size of the dh primes to 4096 bit (closes #527)

[stcz]

I just saw, that this might conflict with scripts/init_letsencrypt.sh

As I understand it correctly, this script should init the nginx configuration, if the configuration path is changed.

[stcz]

scripts/init_letsencrypt.sh should now not be affected, but currently it would download only 2048 bit primes. This should not be a problem.

Another solution might be to remove the files from the repository and create these files with scripts/init_letsencrypt.sh

[m-kuhn]

Thanks @stcz
@suricactus I would suggest we add a freshly generated 4096 bit prime (generated from openssl) and merge