[Core] Provide feedback on loading cases: location clusters

[veuncent]

Build a Report function for input data.

It is possible that input data contains clusters of cases on the exact same lat/long location. This can be of interest to the user, because it can indicate the data do not represent home addresses (but e.g. hospitals).

• Start with building in a feature in the load_cases module that results in a .txt file with all clusters listed in blocks of rows (white lines between clusters).
• When dependent tasks are ready: log these reports to the database