Documentation component + other stuff

The main purpose of this PR is to add a documentation component as a way to fix #331. However, it also contains other changes as I needed to fix stuff on the go, so I recommend revising commit by commit:
- Documentation component added and used for scenes.
- RenameScene action refactored to use scene's documentation component. The RenameTest has also been refactored and it compiles and runs now.
- Bug fix in AddScene. I needed to fix this to get RenameTest running.
- Refactoring of FieldNames. It has been moved to editor-schema so it can be used in exporter