add support for up to 10 ESPNow remotes (#4654)

* add support for up to 10 ESPNow remotes

* removed debug line

* changed todo comment

* fixed some issues, shortened html/java code

- reverting name to `linked_remote`
- ESPNow remote list is now hidden if unchecked
- shortened java script function names and variables to save flash
- removed now obsolete settings in xml.cpp
- correct checking of valid hex string for remote list in java script

* fixed indentation, using emplace_back instead of push_back, using JsonVariant, replaced buttons with +/-

* shortened java code

* updated java code, fixed bug

- element is now properly removed
- `+` button is hidden if list is full
- user needs to remove a remote, then reload the page to add it (workaround for edge case that needs more code to handle otherwise)

* add limit

* clearer usage description

wled00/remote.cpp

@@ -181,16 +181,10 @@ static bool remoteJson(int button)
   return parsed;
 }
 
-// Callback function that will be executed when data is received
+// Callback function that will be executed when data is received from a linked remote
 void handleWiZdata(uint8_t *incomingData, size_t len) {
   message_structure_t *incoming = reinterpret_cast<message_structure_t *>(incomingData);
 
-  if (strcmp(last_signal_src, linked_remote) != 0) {
-    DEBUG_PRINT(F("ESP Now Message Received from Unlinked Sender: "));
-    DEBUG_PRINTLN(last_signal_src);
-    return;
-  }
-
   if (len != sizeof(message_structure_t)) {
     DEBUG_PRINTF_P(PSTR("Unknown incoming ESP Now message received of length %u\n"), len);
     return;