Show save option for framed PDFs when parent page has translator

[dstillman]

In #155 we started showing a PDF icon if there's a PDF in a frame and no translator on the parent page.

Without #152, though, it's not possible to save the framed PDF itself if the parent page has a translator, unless you're using Firefox and can use This Frame -> Show Only This Frame. Even with #152, ideally we would just offer "(PDF)" as an option in the save button context menu when there's a PDF frame, regardless of whether there's a translator on the parent page.

(This will be even more important once we have a generic translator running on all pages, though we'll probably want to try to determine when there's a wrapper page with no content and still show the PDF icon in those cases.)

[adomasven]

This is probably an extreme edge case, but we'll need to work something out if there's multiple frames, probably just rely on #152.