Add config parameters for Pandas Fallback

[westernguy2]

This pull request would add a simple way to disable the catch block that lets Lux fall back to Pandas in the case of an error while running Lux.

Specifically, one would set lux.config.pandas_fallback to False to stop catching errors raised during _repr_html_. One would set lux.config.interestingness_fallback to False to stop catching errors raised during interestingness calculations.

These config parameters are meant for internal dev use and testing.

[dorisjlee]

Thanks @westernguy2 !