Artifactory publish

Publish PR validation artifacts to artifactory so that it can be consumed by the IDE validator. (Only for last commit of a PR.)

How does the IDE validator know which artifact to use?

Review by @huitseeker, /cc @dragos, @lrytz

PS: For the record, this is the ~/.m2/settings.xml we're using (passwords blanked of course)

```
<?xml version="1.0" encoding="UTF-8"?>
<settings>
  <servers>
    <server>
      <id>sonatype-nexus</id>
      <username>lamp</username>
      <password></password>
    </server>
    <server>
      <id>artifactory-bot</id>
      <username>jenkinside</username>
      <password></password>
    </server>
  </servers>
</settings>
```