Apply MIT license to plugin (Java, Jelly and HTML).

After discussion with the maintainers (Francis and Kohsuke), and acceptance
by authors of patches, this patch applies the standard Jenkins MIT license
to this plugin. This was the intended license for this plugin since its
creation, but no indication was placed in the plugin itself of this decision.
Merge pull request #32 from kpfleming/apply-license

Apply MIT license to plugin (Java, Jelly and HTML).