Implemented SSL support for client <-> core connection.

Implemented SSL support for client <-> core connection.
To make this work the core needs a ssl certificate in pem format using
an rsa key. This certificate needs to reside in ~/.quassel/quasselCert.pem

If you don't have a certificate, you can create one using openssl:
  openssl req -x509 -nodes -days 365 -newkey rsa:1024 -keyout ~/.quassel/quasselCert.pem -out ~/.quassel/quasselCert.pem