No organizations support

Consider adding a config option to disable organizations (i.e. just have one organization). hide the organization field in editors etc

For a quick improvement
- [ ] hide organization in the admin tables
- [ ] don't show organizations page in the admin menu
- [ ] config option (`:hide-organizations`)
- [ ] hide "Show only my organization" from lists (see #2046)

For a complete feature we could also do (split)
- [ ] hide in details
- [ ] hide in editors, technically still provide the default organization
- anything else?

Start with the admin tables and admin menu, then trace organization handling in lists, details, and editors. Review issue #2046 for the existing list-filter context and identify where the :hide-organizations configuration should apply. Done means the quick-improvement checklist is covered while the default organization remains available for the complete feature.

Written by the indexing model from the issue text.