Add Maven dependency management

[Noreaster76]

👀 Unless reviewing this on a commit-by-commit basis (rather than on the full diff), don't bother reviewing PR until #217 is merged, since this PR includes commits from the Noreaster76:bit-more-cleanup branch, and it might be too confusing otherwise.

Add Maven, a widely known dependency manager.

(This was attempted in the past in #46, incidentally.)

Benefits / Justification:

• Easier to build and run -- requires just a single command, assuming you have both a JDK and Maven installed (which is common among Java devs)
• Familiar to many Java developers
• Will facilitate future replacement of third-party code by referring to their published artifacts; this will decrease the amount of code within this repo that requires maintenance

[Noreaster76]

@happyjack27 @carlschroedl ?