Allow one to pass "profile" attribute in addition to "css", "js"

Usage:

```
  assetify.addFiles({
    profile: 'core-logged-in',
    js: [
      path.join(privateDirectory, '/javascript/applications/visor/application.js'),
      path.join(privateDirectory, '/javascript/applications/visor/controllers.js')
    ]
  });
```

Allows for more concise code when making heavy use of profiles.