Chat Federation: using S2S if available.

* if both local and remote instance have external XMPP connections enabled, the user joins the remote room with his local account
* some code refactoring (builtin.ts)

Note: documentation and settings descriptions are to do.

Related to #112

conversejs/lib/types.ts

@@ -0,0 +1,23 @@
+interface InitConverseParams {
+  isRemoteChat: boolean
+  localAnonymousJID: string
+  remoteAnonymousJID: string | null
+  remoteAnonymousXMPPServer: boolean
+  remoteAuthenticatedXMPPServer: boolean
+  assetsPath: string
+  room: string
+  localBoshServiceUrl: string | null
+  localWebsocketServiceUrl: string | null
+  remoteBoshServiceUrl: string | null
+  remoteWebsocketServiceUrl: string | null
+  authenticationUrl: string
+  autoViewerMode: boolean
+  forceReadonly: boolean | 'noscroll'
+  noScroll: boolean
+  theme: string
+  transparent: boolean
+}
+
+export {
+  InitConverseParams
+}