Removed all cell imports from `cell/__init__.py`.
Made `OnionTransport` use `shared.transport_manager`.
Merge branch 'MiscToMerge' into RmInitPyImports
Using `shared.py` instead of `shared/__init__.py`.
Merge branch 'MiscToMerge' into RmInitPyImports
Removed __init__.py imports; fixed all imports.