Added SSL Support for OpenVPN GUI

[ashleyj]

This PR adds HTTPS support on port 8081

[kharkevich]

You will get the same behavior if you update app.conf file
For example:

appname = openvpn-web-ui
httpport = 8080
runmode = dev
EnableGzip = true
EnableAdmin = true
sessionon = true
CopyRequestBody = true

HTTPSCertFile=/opt/dehydrated/certs/vpn.example.com/cert.pem
HTTPSKeyFile=/opt/dehydrated/certs/vpn.example.com/privkey.pem
HTTPSPort=443
EnableHTTPS=true

DbPath = "./data.db"