Bug fix: Fed stats fix due to recent simulator changes

[chesterxgchen]

Fixes # . 1) fed_stats is broken due to the simulator changes, change the workspace directory in the notebooks and examples 2) for df_stats job, notice the new datasets has empty line at end, causing pandas to mistaken numerical data type to string type. We change the prepare_data.py to remove empty line 3) update df_stats notebook to add panda data table format.

Types of changes

• [x] Non-breaking change (fix or new feature that would not break existing functionality).
• [ ] Breaking change (fix or new feature that would cause existing functionality to change).
• [ ] New tests added to cover the changes.
• [ ] Quick tests passed locally by running ./runtest.sh.
• [ ] In-line docstrings updated.
• [ ] Documentation updated.

[chesterxgchen]

replace this PR with new one