MultiBlinker, serial debugging restored, and better wifi access point name

[JonathanGiles]

Three improvements:

• My attempt to force the naming discussion - here's a one-line PR to add a more user-friendly wifi AP name. We can change the name, but here's my attempt to lock something in!
• I've also replaced the blinking code for LEDs.
• I've restored the previously deleted serial debugging support.

[lucasnz]

Serial debugging was removed in error in commit c616c82

It was meant to always be enabled on ESP32. Only to be optionally enabled on ESP8266 as debugging used the same serial port as the spa.

[wayne-love]

How do single Led boards display Wifi not connected and Mqtt not connected statuses?

[JonathanGiles]

How do single Led boards display Wifi not connected and Mqtt not connected statuses?

The blink interval increases by a 500ms by each state level. See here: https://github.com/wayne-love/ESPySpa/pull/65/files#diff-48063f99b4c1fbab03ab8d6a5b3b0169d6b7ae52ab36074b2071e9d0dd3963d7R27