Roundtable scenarios summary notebook and results

[eglucas]

Please could you review the new notebook roundtable_scenarios.py - it follows the same structure as report_scenarios_summary_v2.py with some streamlining improvements, as well as another results dataframe that is written in the Excel output with levy rates for each levy and scenario.

The requested scenarios were:

1. Rebalance RO+FiT from Electricity to Gas, increase WHD by a factor of 3.0
2. Rebalance RO+FiT from Electricity to Gas, increase WHD by a factor of 3.0, shift WHD from standing charge to variable (on both electricity and gas)
3. Rebalance RO+FiT from Electricity to Gas, Remove ECO from gas to taxation, increase WHD by a factor of 3.0
4. Rebalance RO+FiT from Electricity to Gas, Remove ECO from gas and electricity to taxation, increase WHD by a factor of 3.0

Please pay special attention to:

• The definition of weights for each scenario
• The creation of a new set of Levies with an uplifted WHD
• The implementation of .apply_social_support_adjustment() to WHD eligible consumers
• The output Excel workbook and that results are as expected

[danlewis85]

add .rename_axis(None, axis=1) to scenarios_summary chain if you want to drop the index column header.

[danlewis85]

I've checked all aspects of the code and it produces the expected results.

Really nice work.