Expose available cipher configuration to node.js (for server)

[bu5hm4nn]

The RFC standards specify a long list of cipher-suites that can be used for DTLS communication.

Expose an optional setting to node-js that can configure which cipher-suites a server will accept. Validate them against the use of PSK and Key authentication. If PSK callback is registered then require at least one PSK-capable ciphersuite to be enabled. If a server key is specified, then require at least one key-capable ciphersuite to be enabled.

Create node-js user friendly defines for the specification of the ciphers. See here for DTLS ciphers https://tools.ietf.org/html/rfc4492#section-6.

Create examples demonstrating at least

1. A PSK configuration where
   a. the ciphersuite requirements are ok
   b. no ciphersuite suitable for PSK is set resulting in a node error exception.

2. A key configuration where
   a. a the ciphersuit requirements are ok
   b. no ciphersuite suitable for key exchange is selected resulting in a node error exception.