Add Web Interface and REST auth

[caco3]

This is an adaption of #2241

It adds basic authentification to the Web UI and the REST API.

There are some important things to know:

• The username/password are transmitted plain text!
• See https://jomjol.github.io/AI-on-the-edge-device-docs/Password-Protection

TODO

• Test
• Provide webpage on denial
• Add documentation to doc repo
  • Note that it only uses basic auth thus it is sent as plain text, see https://stackoverflow.com/questions/9534602/what-is-the-difference-between-digest-and-basic-authentication. Digest ist not supported!
  • show user:password example
• Update changelog