FPM-586 - Remove base flag column

[richjam]

Background

Flag columns previously required a base data column to be specified on creation. This was used in two places: generating a default column name, and auto-including flag columns in select. Neither use case justified the constraint - flags may apply to multiple columns, or to none in particular. This PR removes base entirely from the flag column.

Main changes

• base removed from the flag manager class, and all associated methods
• default column name (in init_flag_column) changed to omit the base column - and added the 'collision avoidance' in case column name already exists
• Removed include_flag_columns from the select method

Note

• Documentation will be modified in another PR