setup.py: include data files in package_data= with paths relative to src/allmydata/web.
Remove packages= entries and unneeded __init__.py files for those subdirectories.

Signed-off-by: Daira Hopwood <daira@jacaranda.org>
Merge pull request #87 from daira/2209-make-pip-install-img-dir

setup.py: include data files in package_data= with paths relative to src/allmydata/web.