use alpha vantage to extract stock information

[GustavoCaso]

Fixes #670

@pitr-ch I created the PR so we can discuss if we like the idea of the user using there own API_KEY for the stock service, or if we want to create one for the repo. Also, there are some missing references to Yahoo in the scala examples I will update once we agree on the best solution or service for extracting the stock information.

[pitr-ch]

I think it would be better for users to have an example which can be executed immediately without any additional setup. Not sure where would we put the API_KEY, it should not be public probably. The examples can also use any API, not just about stock. If there is something similar we could dig from GitHub, it might be simpler.

[pitr-ch]

The scala parts can be dropped.

[GustavoCaso]

@pitr-ch sorry for the delay. I'm will update the code and try finding something that will be simpler without the need to use an API key

[pitr-ch]

no worries! Thanks.

[chrisseaton]

I replaced this PR with #937. It needed some rebasing and better error handling due to the rate limiting in the API.

Going forward I'm not sure we want to really use a service for simple demos. We should mock something out for simplicity. I'm also not sure we want the Scala examples in the repository, as we can't maintain those or check they work.