MainLoop should warn when unexpected argument is passed

[bedapisl]

Migrated from https://github.com/Cognexa/cxflow/issues/206

If somebody passes an unexpected argument to mainloop via the config yaml, cxflow raises an exception stating that the mainloop got an unexpected argument. This can easily happen when copy-pasting some config and ruining some indentations...

This is totally fine, but it's also a bit confusing since the stack trace leads the user through the cli about which the user has no idea (I don't expect regular users to understand mainloop or cli in any depth).

I suggest letting the mainloop accept **kwargs and immediately checking that they're empty. The raised exception should state that configuration file is likely incorrect.