Disabled columns are still shown in exports

[unikitty37]

I tried a CSV export with the Genres column disabled, in order to work around #29:

• Untick Genres under Columns
• Verify that Genres are no longer showing on screen
• Click CSV under Export

However, the exported file still had the Genres column, and columns after that were all messed up in rows that had more than one genre.

I would have expected CSV and XLS exports to honour the user's column selection, and not export those that are not enabled.