no-prod-testing-load:

This patch moves browser-specific test loading to a separate module, which
allows us to exclude all test (and test library) loading in production.  This
should considerably reduce the weight of the application.

Also, the `Makefile` now deletes test files from the build results -- this
should hide our tests from prying end users.  They will still see the loading
stub, but all the actual test code will be gone.