[transaction] PEP8 on module docstring.
[transaction] PEP8 on import.
[transaction] PEP8 misc fixes.
[transaction] Remove old commented code.
[transaction] Use list comprehension.
[transaction] Remove internal awful CamelCase.
Remove broken cookies manager implementation. (#256)

The current cookies manager implementation is broken.
While waiting for a working implementation using the standard library, the
previous implementation is removed.