Adopt reproducible builds

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By default, Maven builds are non-deterministic.

The Reproducible Build Maven Plugin attempts to solve this.

Adopting reproducible builds would potentially yield several advantages, e.g.:

• Memoization
• Improved security
• Easier comparison of build artifacts (e.g. if trying to see whether two artifacts that are ostensibly the same are in all important respects the same, developers could just compare the hashes, instead of having to substitute an entire artifact and run tests, etc). This might help with #1 , by ensuring that each version of each artifact would map to one and only one hash.

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Re-opening, as issue has not been resolved and seems to have been closed erroneously. (Cf. https://github.com/ContentMine/meta/issues/5#issuecomment-308723497 .)