Use sequential loading and requests for all UI resources (#5013)

* use sequential loading for all UI resources

- load common.js and style.css sequentially for all config pages
- restrict all requrests in index.js to single connection
- retry more than once if requests fail
- incremental timeouts to make them faster and still more robust
- bugfix in connectWs()
- on page load, presets are loaded from localStorage if controller was not rebooted
- remove hiding of segment freeze button when not collapsed

wled00/ws.cpp

@@ -157,12 +157,6 @@ void sendDataWs(AsyncWebSocketClient * client)
   // the following may no longer be necessary as heap management has been fixed by @willmmiles in AWS
   size_t heap1 = getFreeHeapSize();
   DEBUG_PRINTF_P(PSTR("heap %u\n"), getFreeHeapSize());
-  #ifdef ESP8266
-  if (len>heap1) {
-    DEBUG_PRINTLN(F("Out of memory (WS)!"));
-    return;
-  }
-  #endif
   AsyncWebSocketBuffer buffer(len);
   #ifdef ESP8266
   size_t heap2 = getFreeHeapSize();