Basic Authentication for the web server

[emlynmac]

Adds HTTP Basic Authentication to the web server in squeezelite-esp32.

By default, disabled.

Set a value in NVS under the http_password key and this will then be needed to access the HTTP server.

Responds to #239.

[sle118]

I'm going to review this soon. Thank you!

[sle118]

I know it's been a little while. Thank you for your patience.

[emlynmac]

I know it's been a little while. Thank you for your patience.

I'm gonna look at the bluetooth PIN situation next. I really need it for my set up...

[sle118]

Still haven't had a chance to do a proper review with competing life priorities. Pin code is problematic because it will likely break most people's configuration. Instead of a pin code, it would be best to instead do something similar to what homeassistant does for pairing ZigBee or zwave devices, which is a "pair" button in the UI (or a hardware button key, like gpio0 that could be bound to that function via the existing JSON configuration for buttons and rotary). Pairing mode would activate for a limited time and associated devices hardware address stored in nvm. This is also how some devices like headsets, Bluetooth speakers, etc. Work