Make www serve default certificate

[popov-vladimir]

Use-case: invite a new network participant just by specifying her IP address, so that API node could get the organization name from certificate subject "field"
One of the best practices is to do such discovery service possible is to serve a well-known URI
To do:

1. make cryptogen save public key to a file msp-admin.pem
2. make nginx serve file msp-admin.pem as /.well-known/msp-admin.pem

[LeonidLe]

well-known URI should be served at http.
According to #33 we are going to serve certificates on API container and therefore open only https, to minimize number of open ports.

After #33 this have to be implemented in the API server in a way both http and https are available