Add functions for better table management

Create table management functions for easy operation on the store, e.g.

    def empty_table(self, table_name):
        """Empty a complete table"""
        pass

    def delete_all_entries_where(self, column_name, value):
        """Delete all entries across the store where an entry with given column_name and value exists"""
        pass

    def reset_store(self, delete_all_entries = False):
        """Reset table rows from table schema. If 'delete_all_entries' is True, the tables will be emptied."""
        pass