Cascading the configuration loader

[0x4007]

I was doing a little refactoring, trying to clean up the configuration loading functions and I realized that we might be able to do something like this:

return { ...fallback, ...organization, ...repository }[key];

To dramatically simplify our configuration loading functions.

The benefit of this is that the built-in defaults fallback are first, then the organization configuration overwrites, and then finally repository configuration does the final overwrite.

This means that the repository configuration will dominate the rest, for example.

Is this implementation a bad idea?

Context: a6ef97a#diff-d9b0865f2e8f841410cd4faf3e1e4a1fb7cb0b545f583f6adaad5841d7eaa58dR52

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We can do this using lodash function merge (example)

Originally posted by @whilefoo in #648 (comment)