Add support for basic authentication for the web server.

[psa-jforestier]

For my personal use, I added the "basic-auth" authentication mecasism in RPi-Monitor. When enabled, if you go to the web interface, you will be prompted for a user and password (HTTP 401 response). If the user/pass match the one in config file, you will get access to the ressource. Otherwise, you will get a new HTTP 401 response requesting a user/pass. All browsers support "basic" auth, where the user and pass is send to the server in plain text (base64 encoded), so it is not suitable if you dont trust the network.

[XavierBerger]

Thanks for the pull request. I need to validate it before merging but this is a nice feature for RPi-Monitor.