Secure api server

This PR relates to issue: https://github.com/jembi/openhim-core-js/issues/205
NB! This PR needs to be merged when the console changes are merged (https://github.com/jembi/openhim-console/pull/151)
The above is only needed for mutualTLS (ie both the client and server nneed to supply a certificate). We don't need this for the API. We just need our server to have a certificate to use for HTTPS. I'd suggest just creating your own options object here that defined the `cert:` that the server should use.