Rename module test
Add module context test
Add src/js/embed.js

Rename test_embed_element.js -> embed_for_testing.js
Add QueuingEmbed and tests

This embed element will queue messages until the module is loaded.
Add delegation to QueuingEmbed and tests.

Not sure if I want to keep this though; it is more complicated than it
probably needs to be.
Remove files from the old prototype.