Improve catalogue handling

[MatthewWhiting]

The API for handling the columns of a catalogue should be improved. It would help Selavy development to have more transparent classes that handle both single columns and a catalogue (being a collection of columns) -- rather than the current approach of using a simple vector and a host of const arrays and enums.

This should go well with the catalogue writing classes to make it all more easily handled.

[MatthewWhiting]

Commit [1061] has a large amount of code that implements the first stage of this. To summarise:

• columns.cc,hh moved to Outputs
• The class Col renamed to Column, and put in a new namespace Catalogues.
• The API changed slightly, such that the type of the column is recorded as a string, rather than using the enumeration. This allows flexibility in adding new column types
• A new (unimplemented) class CatalogueSpecification? defined to act as a generic holder of a group of columns.

The code with this change still passes all the verification scripts, so the formatting of the results and log files is still identical to the 1.2 version.

[MatthewWhiting]

This is now fully implemented. There has been no functional change (thanks to improved verification scripts that now check the XML/VOTable output), but the code is a bit more modular and cleaner.

This can be closed!