Add Logger to library

[klenotiw]

Description

This PR moves the logger we had in shopify_app into the api library. This ensures that our logs are consistent across both repos.

How does it work?

Almost everything is the same but instead of storing the log level in ShopifyApp::Configuration, it's stored in ShopifyAPI::Context. So now if developers what to change the log level they would need to change it in their Shopify::Context.setup(...) call. Which lives in the same file as the shopify_app configurations. (config/intializers/shopify_app.rb)

I switched the Logger module to a class. This lets shopify_app create its own logger class and inherit its functionality, and override areas that deviate. For example there is no way to compare the version number in the shopify_app if the logger lives solely in the api. Also we should have a slightly different context method. Where the api would have "ShopifyAPI" as a prefix and the shopify_app would have "ShopifyApp". This will help developers know where exactly these logs are coming from.

I also made some error classes, FeatureDeprecatedError and LogLevelNotFound for the errors that we raise in methods found in Logger. Hopefully this gives some good hints on what is going on when the logger raises an error.

How has this been tested?

I also made a test file in test/logger_test.rb which does some unit tests on most of the logic found in the Logger class.

Checklist:

• My commit message follow the pattern described in here
• I have performed a self-review of my own code.
• I have added tests that prove my fix is effective or that my feature works.
• I have updated the project documentation.
• I have added a changelog line.

[nelsonwittwer]

Glad to see this functionality in the API! 🎉 🍻 Hopefully these changes don't take too long and make sense. If not, let me know and I'll be happy to help ya!

[cquemin]

Some question around consistency of deprecated log message/configuration as I already mentioned on your other PR

[klenotiw]

If I could approve I would. Thanks Nelson for the additions!

[cquemin]

Awesome work guys! This looks pretty good!