Jenkins continuous integration (CI) jobs and configuration

The Jenkins jobs running [over here](https://ci.inria.fr/sos/) test the latest snapshot of Spoon on a variety of projects, in a variety of ways. There are two general kinds of jobs:

* For projects that use Spoon
- Inject the latest Spoon snapshot and run project's test suite
- Uses the new [inject_spoon_snapshot.py script](https://spoon.gforge.inria.fr/jenkins/inject_spoon_snapshot.py)
* For projects that don't use Spoon
- Parse and pretty-print the project with spoon-maven-plugin using the latest Spoon snapshot
- Then run the project's test suite

There's a bunch of tiny details surrounding this as well. In order to facilitate for someone else to manage Jenkins (or just myself next week when I've forgotten all about this), we should 1) streamline the jobs to make it very easy to add a new one, and 2) properly document how everything works.