Exclude package private classe references from entry points assertions

Since 2.2.0, when includePackagePrivateClasses option is enabled, package private assertions classes are referenced in the entry points assertions classes, like BddAssertions...
Which can cause compilation errors when these entry points classes are not generated in the same package.

As workarounds, the following plugin [configurations](http://joel-costigliola.github.io/assertj/assertj-assertions-generator-maven-plugin.html#configuration) can be applied :
- entryPointClassPackage configuration could match the package which contains assertions for package private classes
- entry points assertions classes generation should be disabled

Ideally, package private classes should not be referenced in entry points classes