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/wled.h

@@ -538,7 +538,8 @@ WLED_GLOBAL bool     serialCanTX _INIT(false);
 WLED_GLOBAL bool enableESPNow        _INIT(false);  // global on/off for ESP-NOW
 WLED_GLOBAL byte statusESPNow        _INIT(ESP_NOW_STATE_UNINIT); // state of ESP-NOW stack (0 uninitialised, 1 initialised, 2 error)
 WLED_GLOBAL bool useESPNowSync       _INIT(false);  // use ESP-NOW wireless technology for sync
-WLED_GLOBAL char linked_remote[13]   _INIT("");     // MAC of ESP-NOW remote (Wiz Mote)
+//WLED_GLOBAL char linked_remote[13]   _INIT("");     // MAC of ESP-NOW remote (Wiz Mote)
+WLED_GLOBAL std::vector<std::array<char, 13>> linked_remotes; // MAC of ESP-NOW remotes (Wiz Mote)
 WLED_GLOBAL char last_signal_src[13] _INIT("");     // last seen ESP-NOW sender
 #endif