R1:27227b8010ee

Show missing Phriction documents as red links, invisible documents with a lock

Summary: Ref T7691 (errata). This shows links to Phriction documents in red if they're missing, and links to Phriction documents in grey with a lock icon if the user doesn't have the correct permissions to see the document.

Test Plan:
Tested a bunch of different configurations:

```
[[ ./../ ]] Back to Main Document
[[ ./../subdocument_2]] Mmmm more documents
[[ ./../invisible_document]] Mmmm more documents

[[ ./../ |…