adding the deploy_helper module

After a discussion on the ansible-project mailinglist, this module was formed to help lower the boilerplate needed to deploy web-projects.
See the thread here: https://groups.google.com/d/msg/ansible-project/R3Kr2uMYUt4/b-WLJ3m6L1AJ

This pull request will be accompanied by an additional guide for the documentation, I will link it as soon as I have it up.
Until that time, the documentation for this module contains an invalid link to doc:`guide_deploy_helper`