Hotfix: Turn 'cod' into 'cash_on_delivery' when WGM is loaded

[ScreamingDev]

What has changed?

• wcsc_get_cod_id function
• uses filter to allow manipulation
• compatibility for WGM

Things to review

Common things:

• [x] Works fine.
• [x] Changelog written or not needed.
• [ ] In case of bugfix also merged in other minor versions.
• [x] No conflict with current branch.

Got an idea while looking at the GUI? Please add a new issue refering to this one.