Enable the plugin to support multiple versions of checkstyle

As has been mentioned under https://github.com/m2e-code-quality/m2e-code-quality/issues/222 it would be useful for the checkstyle plugin to be able to run the specific version of checkstyle that is used in the configuration of a project.
At present an Eclipse user needs to install a single specific version of the eclipse plugin which may not correspond to that used in the various projects that they work on. This can lead to either errors being reported by the plugin but not actually present in the build or vice-versa.