[WIP] Array improvements for mapper

Needed abilities for content form generator:

- [ ] Array for value only
- [ ] Add Element
- [ ] Remove Element

Checklist:

- [ ] test coverage
- [ ] finish the code
- [ ] gather feedback for my changes
- [ ] submit changes to the documentation


| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | yes
| Tests pass?   | none
| Fixed tickets | none
| Doc           | [url to doc|none]