There are several files we need these days for building and testing the

Djblets packages which weren't included in the source distribution. This

includes the static media toolchain, the unit test configuration, and

the tox file.
This change adds all these to the manifest, ensuring they're there in

the tarball. It's a precursor to further work on the Djblets packaging.

Built a source distribution and verified the package contents.
Tested this along with in-progress package management code, and managed

to build wheels from the source distribution that were identical to

wheels built from the tree.