Add support for more documents

chains.py updated
All the files in data/urls.txt are cleaned and imported successfully.
Add 'auto' subcommand to import_data.py

Plus a number of smaller changes to data_import/data_import.py
and a general restructuring of import_data.py
Remove print() and fix wipe bug
Update documentation of import_data stuff

Added intro to the new subcommand 'auto' in import_data.py.
Add bet-2002-2005.sql.zip
Fix error in docs for data import
Merge branch 'import_data' into develop