Refactor

[asmeurer]

Clean up the code a bit now that we have multiple functionalities.

Code changes

• Each check now has its own function.

Functionality changes

• GET requests are now cached. With the refactor some requests would be called multiple times otherwise.
• The added/deleted check is no longer done on a "merge" action.

[asmeurer]

Still not quite sure how to clean up the tests. We should probably merge this as-is.