Custom scaffold templates - POC

This code adjustment and the new global config makes it possible have your own simple extended plugin or other templates if implemented for the Unit tests.

`wp scaffold plugin zombieland --author='Jaime Martinez'`

`~/.config/plugin.mustache` :
```
<?php
/*
Plugin Name: {{plugin_name}}
Version: 0.1-alpha
Description: PLUGIN DESCRIPTION HERE
Author: {{author}}
Author URI: YOUR SITE HERE
Plugin URI: PLUGIN SITE HERE
Text Domain: {{textdomain}}
Domain Path: /languages
*/
```
`wp-cli.yml` :
```
scaffold plugin:
  template_path: '/Users/jmslbam/plugin-x.mustache'
```

- [x] CPT with tests
- [x] TAX with tests
- [x] Plugin with  tests
- [x] Proper trigger a no file exists error
- [ ] Child theme?

Out of scope, after merging of master
- [ ] Proper call get_home_env everywhere?
- [ ] Use `absolutize` from `\Utils` in `Configurator.php`?

**var / args (template_path)**
So there will be a `--template_path` arg per commando so it can be overwritten per scaffold command or set in the `wp-cli.yml` config file.