Pandas version fix

[xandaau]

In the requirements we have pandas version >=0.24.0, however some code in Designer class (actually pivot_table method) crashes when pandas version is less than 1.3.0.

This is needed to be fixed, and can be done in two ways:

1. Upgrade pandas version in requirements and check that everything is okay
2. Rewrite code for pivot_table() and leave the appropriate version of the dependency as the older one

Short error snippet

get_empirical_table_sample_size
    report = report.pivot_table(
TypeError: pivot_table() got an unexpected keyword argument 'sort'