Deploy snapshots from Travis CI to Artifactoryonline

I create this pull request to test the conditional `mvn deploy` (should be disabled on pull request validations). But I'll merge it anyway to master in order to start CI for jobroom-api.

Following possible improvements are still pending:

[ ] re-introduce the build with OpenJDK7 => push artifacts from only a specific build (e.g. JDK8), but only if all the builds succeed (`after_success` hook should do the trick...)
[ ] optimize the test sequences (3 different DBMS)
[ ] fine tuning of Snapshot / Release shipping conventions (e.g. create dedicated branches?)
[ ] Why not overwrite snapshot artifacts instead generating timestamped artifacts?