POM-4. Add kiji-annotations library to dependency management section of ...

...root pom.

This commit adds the kiji-annotations library, used by Kiji projects to annotate
classes with audience and stability information, to the root pom. This is to ensure
consistent version usage throughout Kiji projects.

Tested the change by running mvn install on this project.  Then, kiji-schema was modified to comply with this change and mvn verify was run on that project successfully.