Feat: Allow template name to be configurable.

This patch is similar to #33 in that it allows the template name to be configurable. Ex:

```
ngtemplates:    {
  templateConfig: {
    options: {
      templateConfig: function (file) {
        return path.join('foo', file);
      }
    },
    src: ['test/fixtures/simple.html'],
    dest: 'tmp/template_config.js'
  }
}
```

Will prepend all template names with the string ```foo/```.

This allows template name configuration to live in the ```Gruntfile```. If this config is not set, then the other options (```prepend```, ```base```) will be used like before.