Note that as discussed on IRC, this makes the viewer slightly slower to load *only* in `gulp server` mode, however the difference seem slight enough that I think it will be fine.
Instead of just upstreaming the changes from [bug 1345253](https://bugzilla.mozilla.org/show_bug.cgi?id=1345253) as-is, it seemed better to simply get rid of the loops altogether and use the same approach as in `PDFViewer`/`PDFThumbnailViewer`.
This not only reduces code duplication, but it also allow us to easily support the same kind of URLs we currently do for Link annotations in the Outline as well.
Changes `PDFOutlineView`/`PDFAttachmentView` to be initialized once, since we're always creating them, and refactor their `render` methods to instead pass in the `outline`/`attachments`.
For consistency with other "classes", the `PDFOutlineView`/`PDFAttachmentView` are renamed to `PDFOutlineViewer`/`PDFAttachmentViewer`.
Also, make sure that the outline/attachments are reset when the document is closed. Currently we keep the old ones around until the `getOutline`/`getAttachments` API calls are resolved for a new document.