mako_requirements

I couldn't run the demo app without installing some extra requirements and adding some configuration.

This pull includes the following changes:

- add a `requirements.txt` to top-level working directory to declare dependencies
- include `python_mako` package into "Demo 0" app.

To run the "Demo 0" project I have to do the following (assuming `virtualenv` is installed):

```bash
$ mkvritualenv --no-site-packages pyramid_auth_demo
$ pip install -r requirements.txt
$ cd demo0
$ python demo.py
```

This issue probably affects the other demos, but I haven't used them yet.