Initial playbook

This is an Ansible playbook for the IPython project's Jenkins server. This playbook:

* installs Jenkins via [ICTO/ansible-jenkins](https://github.com/ICTO/ansible-jenkins) (as a role, through a git submodule)
* installs some base plugins for Jenkins
* puts Jenkins behind nginx
* 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?).