Rename main bundle outputs

This looks a bit better:
  hypothesis.min.js and hypothesis-inject.min.js
Handle SCE better with custom base URI

When we deploy as an extension the application baseURI is the URL
of the backend, rather than the extension. As a result, templates
are relative to this location. Even though we inline the templates
in the extension bundle, we have to ensure the compilation isn't
blocked by strict contextual escaping.
whitespace
Don't copy all libs to extension, just images

This avoids getting all the un-minified js
Add pdf.js as a submodule
Include pdf.js from extension build script

With this change, I have no problem testing a local chrome extension
build.

Close #891