Replace socket.io with plain WebSocket

Replace socket.io with plain WebSocket using the ws library as it
doesn't really provide any useful tools over plain WebSocket when it
comes to implementing reliable communication that works across
reconnects.  The widespread browser support for WebSocket also means
it has little value to add for the web interface over WebSocket.

package.json

@@ -61,10 +61,9 @@
     "set-blocking": "^2.0.0",
     "simple-git": "^1.96.0",
     "single-line-log": "^1.1.2",
-    "socket.io": "^2.2.0",
-    "socket.io-client": "^2.2.0",
     "sync-request": "^4.0.1",
     "typescript-collections": "^1.3.2",
+    "ws": "^7.2.3",
     "yargs": "^14.2.0"
   },
   "devDependencies": {