[update of SandwichFeatures]
- added 'min_dis_between_sheets_by_all_res' column to see a relationship
between 'min_dis_between_sheets_by_all_res' and 'holes' (surprisingly,
no relationship found)
- refactored SandwichFeatures much more by introducing WriteToDBFromSandwichFeatures.cc
- should not change any integration tests other than (expected) features and features_database_schema (if any)