Improve on the Swagger doc

[ateska]

• change in build_swagger_documentation so that it propagates a host into the list of servers; it is more sane way of how to call "self" from Swagger, removing that relative URL
• improved way of how swagger is loaded to web server (thru index.html)
• added "shortcut" param "api" to asab.web.create_web_server() that enables swagger doc just by stating api=True

[mejroslav]

@ateska Can you summarize what this is about and if there are gonna be some TODOs?

[ateska]

Summarised.

[ateska]

Flake8 is broken, no other TODOs on the list.
Maybe re-alignment with the recent Swagger changes will be needed.

[ateska]

Flake8 is working now but the unit test in Python 3.9 is failing.

[mejroslav]

Flake8 is working now but the unit test in Python 3.9 is failing.

That is probably ok. The unit test was designed to expect a different output from this function. I disabled it in master.

[mejroslav]

OK, I am taking this one.