Split jenkins from non-jenkins code

This is a suggestion for a split that would allow the creation of a jar with the parsing code, that in turn would be used by the jenkins plugin as a dependency. All the classes inside the package `com.ullihafner.warningsparser` represent the classes that are not dependent on jenkins code.

Please, could you take a look and see if this seems like a good approach for you.

(this is a first step towards [JENKINS-17434](https://issues.jenkins-ci.org/browse/JENKINS-17434))