Add maven wrapper

[HugoMario]

We're getting build success in maven but there is an error because an expected file (mvnw) is missed.

travis_time:end:0b887d28:start=1517960823002986545,finish=1517960852615714515,duration=29612727970
�[0Ktravis_fold:end:install
�[0Ktravis_time:start:19493319
�[0K$ ./mvnw clean verify
/home/travis/.travis/job_stages: line 57: ./mvnw: No such file or directory

travis_time:end:19493319:start=1517960852623041063,finish=1517960852630086436,duration=7045373
�[0K
�[31;1mThe command "./mvnw clean verify" exited with 127.�[0m

Done. Your build exited with 1.