FEAT: Add twig task

## new Twig templates render

Add a new file called twig.js in your configs folder with the following
content

```javascript
module.exports = function ( grunt, pkg ) {
  'use strict';

  return {
    'chrome-app': {
      opts: {
        // make the files be relative to this folder
        // so when copying the relative structures is honored
        cwd: 'src/pages/',
        // the data to be passed to the templates
        data: {}
      },
      // the files to be processed with twig extension
      src: ['src/pages/**/*.twig'],
      // the path where the files are going to be copied to
      dest: 'generated/pages/'
    }
  };
};
```
ENH: Specify custom tasks to run during prepush

Now it is possible to specify other tasks apart from the validation
ones (jsbeautifier, jshint, jscs, jsvalidate) to be executed during the
pre push hook.

in your `common-config.js` file add the following entry
```javascript
prepushTasks: [ 'jsontlint' ],
filesTovalidate : { … }
```

The above can be used to execute other custom tasks during the pre push
hook