move js-jetpack to js-jetpack-module-slow

Running sjcl as a normal jetpack module is 20x slower than it should be.
copy in code from my kdf-pageworker branch, to make it run fast

Will adapt to a proper module API. This uses the "create a page-worker,
which creates a web-worker" approach, which appears to work around
whatever the JS environment bug is that causes normal modules (and
normal page-workers) to run 20x slower than content contexts.
remove unused files, will be replaced with other stuff
working on module-ifying, still broken