User configurable SSL settings

Adds user configuration for the following Erlang SSL settings:

* secure_renegotiate (default = false)
* ciphers (default = whatever that version of Erlang decides, possibly [this](https://github.com/erlang/otp/blob/07b8f441ca711f9812fad9e9115bab3c3aa92f79/lib/ssl/src/ssl_cipher.erl#L228))
* version (default = sslv3 - tlsv1.2)

This is useful immediately because Erlang less than R16B03-1 has incorrectly implemented handshaking with elliptic curves, causing hard to debug SSL errors in recent versions of Chrome, Safari, Firefox, curl and go (in a very incomplete list).

It also allow administrators to change the priorities of ciphers for their installation or remove ciphers in the wake of attacks.