Move static folder out of the Python module tree

Currently in swh-web source code, the static folder is located in the swh/web/ Python source tree.

It could be moved in the root folder of swh-web as this directory does not contain any Python code but rather image files but also webpack generated bundles.

This will imply adjusting Django configuration and MANIFEST.in content to locate static assets.

Also, the packaging of those files will need to be updated (likely by using this setuptools feature)

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Migrated from T2155 (view on Phabricator)