Support for multiple instances with different configurations

Introduces a command-line switch -c config-id or --configuration config-id.
This allows you to run multiple instances of swyh-rs where each configuration can use a different audio source.
Suggested by @cavadias, see issue #82.
Each configuration gets its own config file and log file in the .swyh-rs folder in your HOME directory, identified by the config-id (blank by default).
The delay when starting the webserver is removed as it can interfere with autoreconnect.

Windows binaries and setup, and Ubuntu 20.04 LTS and later (and Ubuntu derivates) appimage in assets.