This module was only used to assist testing, but wasn't actually
available in a test environment where no copies of nilmrun have been
installed.  Just code the contents directly into the filters that the
tests are running.

Non-embedded mode is not used in the test suite or wsgi server;
it was an option in the standalong nilmdb-server script, but it's
really not necessary, and removing it gets rid of some untested
code.

Multiprocessing and Apache's mod_wsgi don't play nicely.  Switch to
manually managing processes via subprocess.Popen etc instead.  When
running arbitrary code, we write it to an external file, and running
functions directly is no longer supported.

Now an entire process tree is killed in /process/remove, as long as
each child hasn't changed its process group.