Add different boilerplate templates

[davidomarf]

Add a list of boilerplates that gets called when you run ginpar init in a wat of prompts. They could be anidated:

A boilerplates list like this:

.
└── Boilerplates/
    ├── p5/
    │   ├── grids/
    │   │   ├── sketch.js
    │   │   └── data.yaml
    │   └── particles/
    │       ├── sketch.js
    │       └── data.yaml
    └── d3/
        ├── sketch.js
        └── data.yaml

Would result in this series of prompts:

$ ginpar init

1. p5
2. d3

Select a boilerplate: 1

1. grids
2. particles

Select a boilerplate: 2

Choose the name of the new project: Example

> Creating `Example` using `p5/particles`