Add maven-wrapper and configure CI to use it

[bdemers]

NOTE: also disable verbose artifact download messages (~40% of the log lines)

[coveralls]

Coverage remained the same at 100.0% when pulling 8f8be59 on mvn-wrapper into 5339faf on master.

[lhazlewood]

What's the benefit of this? Why is it important to add/adopt and maintain this approach moving forward?

I don't ever really use the maven wrapper, so I'm just curious on why it's necessary or valuable. Looking forward to learning!

[bdemers]

IMHO, the biggest reason is for CI consistency. The version of Maven installed is no longer dependent on what Travis provides (and because of this is less suspectable to any unexpected change of behavior between environments), i.e. we are now pinning the builds to use Maven 3.6.1

By updating to Maven 3.6.1 (we can remove the transfer log spam with the new -no-transfer-progress flag), granted there are other ways to install a given version of Maven, this is just the easiest.

The Maven Wrapper also lowers the barrier of entry for some projects. Assuming you have Java installed you could build any project that uses the wrapper.