apiserver: Serve web ui

spiderpig/api.py:
Add routes for /, /login, and /jobs/{job_id}, all of which deliver
web/dist/index.html.

MANIFEST.in:
This file is used in two modes. When building a source dist, it is
used to determine what extra files are included in the sdist. When
building a wheel, it is used to determine what extra files are
included in the wheel, but only files that are contained within a
Python package are considered.

setup.py:

• Run npm install and npm run build before the stock build stuff. This
  will populate the web/dist directory.
• Added include_package_data=True which causes MANIFEST.in to be processed.
• Added web.dist and web.dist.assets packages to packages. These are
  effectively references to the web/dist and web/dist/assets directories.
  Because neither of these directories contain __init__.py, these are
  considered to be "namespace packages".
• Removed unnecessary package_dir={"scap": "scap"}.