Enable all repos to aggregate contributors

[tbookless]

Question from @dblevins: "What section of the code would we need to poke at to enable all https://github.com/microprofile/* repos to aggregate contributors together for the http://microprofile.io/contributors page and NOT yet publish them on http://microprofile.io/projects ?"

Answer from @tveronezi: "In the ServiceGithub class, we need to create a new method that lists the microprofile organization repositories (https://developer.github.com/v3/repos/#list-organization-repositories); Then we call https://github.com/microprofile/gitpress/blob/master/src/main/groovy/io/microprofile/ServiceGithub.groovy#L70 for each repository and combine the resulting lists.