Refactor WebSocket message interfaces

Changes:
- Replace AccountTextMessage with an extendable ContactMessage interface
- Add accountId parameter to server-side WebSocket callbacks
- Set the accountId for WebRTC messages on server-side for security
- Rename all WebRTC and SDP variables to proper camelCase or PascalCase

GitLab: #147
Change-Id: I125b5431821b03ef4d46b751eb1c13830017ccff
diff --git a/common/src/enums/websocket-message-type.ts b/common/src/enums/websocket-message-type.ts
index 1152101..04a1f90 100644
--- a/common/src/enums/websocket-message-type.ts
+++ b/common/src/enums/websocket-message-type.ts
@@ -18,11 +18,11 @@
 export enum WebSocketMessageType {
   ConversationMessage = 'conversation-message',
   ConversationView = 'conversation-view',
-  WebRTCOffer = 'webrtc-offer',
-  WebRTCAnswer = 'webrtc-answer',
-  IceCandidate = 'ice-candidate',
   CallBegin = 'call-begin',
   CallAccept = 'call-accept',
   CallRefuse = 'call-refuse',
   CallEnd = 'call-end',
+  WebRtcOffer = 'webrtc-offer',
+  WebRtcAnswer = 'webrtc-answer',
+  WebRtcIceCandidate = 'webrtc-ice-candidate',
 }