Drag in Python llsd module, which greatly simplifies tests.

It only took a few examples of trying to wrangle notation LLSD as string data
to illustrate how clumsy that is. I'd forgotten that a couple other TUT tests
already invoke Python code that depends on the llsd module. The trick is to
recognize that at least as of now, there's still an obsolete version of the
module in the viewer's own source tree. Python code is careful to try
importing llbase.llsd before indra.base.llsd, so that if/when we finally do
clear indra/lib/python from the viewer repo, we need only require that llbase
be installed on every build machine.