Add Java API for the Git module + new APIs

    /**
     * Find all authors who have ever committed code in the passed repositories.
     *
     * @param repositories the list of repositories in which to look for authors
     * @return the list of authors who have ever contributed code in the passed repository
     */
    Set<PersonIdent> findAuthors(List<Repository> repositories);

    /**
     * Count commits done by all authors in the passed repositories and since the passed date.
     *
     * @param since the date from which to start counting. If null then counts from the beginning
     * @param repositories the list of repositories in which to look for commits
     * @return the author commit activity
     */
    UserCommitActivity[] countAuthorCommits(Date since, List<Repository> repositories);