Switch to a bootstrap script and re-include pdf.js

Include PDF.js generic build with only one addition of our script tag.
Strip all the non-essentials from the manifest.
Refactor embed.js and put the bootstrap code into a bootstrap.js with
a corresponding destroy.js inside h:static. These expect globals for
`hypothesisRole` and `hypothesisConfig` rather than using query
parameters. The base URI is determined by adding a link tag with
rel="sidebar" to the page. In this way, the Chrome content script
environment in embed.txt can export what the yepnope loaded scripts
will need in order to bootstrap.

PDF.js is the generic build v1.0.68