Allow dispatch to follow packages to resources

Summary:
This will allow us to get resources from other packages.

Currently it will only work on the base level;

```
$this->requireCss("#components/auth#test");
```

Test Plan: Include some external resources

Reviewers: brooke

Reviewed By: brooke

Maniphest Tasks: T73

Differential Revision: http://phabricator.cubex.io/D11