Sort and deduplicate username blacklist

Also convert to a plaintext newline delimited file -- there's nothing
gained from using YAML here at the moment.
Validate at registration that username is not blacklisted

This adds a validation rule in the registration schema that prevents
users from registering with blacklisted usernames.
Lazy-load username blacklist

By lazy loading the blacklist applications can include the h package
and subsequently use the `config.override_assets` API to change the
blacklist file before the first request.
Merge pull request #1571 from hypothesis/username-blacklist

Username blacklist
Fix race in chrome injections

Close #1568
Add PDF.js assets to the Chrome extension

This comes from PDF.js v1.0.473, generic build, with zero modification.
Insert H code into the PDF.js viewer html
Fix URI and metadata handling for PDF documents

Don't load the Document plugin for PDF files; Annotator's PDF plugin
provides the fuctionality (uri+metadata extraction) in these cases.
When displaying annotations, avoid non-clickable URIs
Modify background.js for PDF.js

inject and remove logic has been modified to handle
PDF.js differently.
Update Chrome extension manifest.json

Remove a bunch of useless permissions,
update a few filenames
Always copy bootstrap and destroy in extension