ORTC: Add basic data channel constructors

Resolves #273

rtcdtlsparameters.go

@@ -0,0 +1,7 @@
+package webrtc
+
+// RTCDtlsParameters holds information relating to DTLS configuration.
+type RTCDtlsParameters struct {
+	Role         RTCDtlsRole          `json:"role"`
+	Fingerprints []RTCDtlsFingerprint `json:"fingerprints"`
+}