Simplify apkSorter using compare-func package

[raphinesse]

Motivation and Context

When reviewing #779 I had a hard time understanding what the behavior of apkSorter was. I find that is a common issue with complex sort callbacks in JavaScript.

IMHO it's often makes for way more readable and less repetitive code to have a sortBy style approach. That's what I implemented in this PR for apkSorter.

Description

Implement apkSorter in a sortBy style using the compare-func module.

Testing

I used the existing unit tests. One of them had to be fixed, since it stubbed fs.statSync incorrectly (mtime is a Date, not a timestamp)

[erisu]

👍 LGTM