Plugit

Introduction of the `PI_USE_PROXY_IP` setting, allowing PlugIt services to do remote ip check behind a proxy.

Fix django methods used to resolve the hostname to take into account possible usage behind revers proxy server.

Small fix for proxy, when not used in standalone mode

Major update with new architecture of the project.

* `Dockerfile` to run examples
* Renamming of `client` to `proxy` and `server` to `service`
* PlugIt proxy and service usable as a library, instead of copying the code localy to a project
* New tests
* Multiples bug fixes
* Updated examples

As a service, you can now remove your local plugit folder and use the `plugit` library instead (`pip install plugit`).
If you had a `mail` function in `plugit/routes.py`, you can move it to your local `actions.py` file and pass the function to the `load_actions`.
Everything else should be compatible with previous versions.