Support a runx method supporting a hypercorn config file

[netomi]

This PR proposes the following changes:

• remove hack wrt __main__.__file__ to determine the app dir
• support an app_dir kw arg to override the app directory if needed, defaults to the cwd
• pop asfquart specific kw args prior to calling super.init as quart panics otherwise
• add a runx_from_config method to support running hypercorn with a config file

That allows to run asfquart with a hypercorn config file to set various settings that would otherwise not be possible, e.g. --reload.

[netomi]

Not sure about the runx_from_config method anymore. My idea was to have a way to run an asfquart in development mode. For that the watch mechanism is not useful at all, looking for other ways to support that.