[BUILD] use mvnw (maven wrapper)

[bmarwell]

Adds mvnw.

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Old description:

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Still fails the build, but error is unrelated to this change and fixed by #58.

I think this should be rebased on: #58 (or vice versa).

Luckily, the error is revealed by one of my latest contributions 😉

Native git invocation failed. Command: /usr/bin/git commit -m Hello George --author='Sandra Parsick <sandra@*****.com>', return value was: 128

[mavenjdk8:2164] stdout was: 
[mavenjdk8:2165] stderr was: Committer identity unknown
[mavenjdk8:2166] 
[mavenjdk8:2167] *** Please tell me who you are.
[mavenjdk8:2168] 
[mavenjdk8:2169] Run
[mavenjdk8:2170] 
[mavenjdk8:2171]   git config --global user.email "[email protected]"
[mavenjdk8:2172]   git config --global user.name "Your Name"
[mavenjdk8:2173] 
[mavenjdk8:2174] to set your account's default identity.
[mavenjdk8:2175] Omit --global to set the identity only in this repository.
[mavenjdk8:2176] 
[mavenjdk8:2177] fatal: unable to auto-detect email address (got 'root@0e5559c167a9.(none)')

[bmarwell]

Blocked by: carlossg/docker-maven#301