Don't check style in resources that are not on the class path

Fixed #10. Filter out resources that are not on the class path
of a Java project (class path includes source path). Even though
there are convenient methods on `ScalaProject`, I relied on
`JavaCore` so that I don't introduce a dependency on Scala IDE.
Merge pull request #11 from dragos/issue/dont-check-non-src-folders

Don't check style in resources that are not on the class path