Initial playbook

This is an Ansible playbook for the IPython project's Jenkins server. It installs Jenkins via [ICTO/ansible-jenkins](https://github.com/ICTO/ansible-jenkins), some base plugins for Jenkins, puts Jenkins behind nginx, and installs some development dependencies.

We'll need a server certificate and key for this box. For now I can use a self signed key while I test this out and we get going.

It's highly based off a playbook written by @smashwilson and (slightly modified by) me. :clap: Thanks Ash! :clap:

@takluyver and all - let me know what else we need here for development dependencies as well as Jenkins plugins.

Next steps *not* covered in this PR:

* Build scripts
* Windows slave building

Those will come separate from this PR and possibly just put manually in Jenkins (yuck?).