Clean-up mess with custom order id setting

[bernhard-wunderbyte]

In shopping cart, there currently is a setting called cashreportshowcustomorderid.

We should get rid of this setting.

Instead, the cash report should show all IDs (like tid, merchantref and customorderid) as different columns.

As this requires a lot of SQL refactoring, I decided not to start with this yet, but in the future, this might be really necessary, so we do not create unreadable code.