Some pylint errors are worth fixing; many are not.

With this solution, we can catch it cleanly in the standalone
nilmdb-server, and test the error paths in our normal test suite.

It works again now.

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.

Enable the following pragmas: synchronous=NORMAL, journal_mode=WAL.
This offers a significant speedup to INSERT times compared to
synchronous=FULL, and is roughly the same as synchronous=OFF
but should be a bit safer.

"import nilmdb" doesn't do much; "import nilmdb.client" or "import
nilmdb.server" is now required.

These functions can now take an object or a type (class).

If given an object, they will wrap subsequent calls to that object.
If given a type, they will return an object that can be instantiated
to create a new object, and all calls including __init__ will be
covered by the serialization or thread verification.

This is quite a bit simpler than the class decorator method, so it
may be more reliable.