Logic to create feature importance is not using the correct model

[sharathmalladi]

The feature importance should not use a model file that is prior to the policy reset date.

[sharathmalladi]

Sharing more context on the current logic:
When a counterfactual evaluation is created with a start and end date, we currently use the model file that was saved on the start date as input to vw to run the feature importance:
https://github.com/microsoft/mwt-ds/blob/master/DataScience/ExperimentationAzure.py#L168

This is not the right thing if the model or policy was reset in between the evaluation period and the logic needs to be tweaked to adjust for that.