Editor Section/Properties: Warning symbol for identical names

- When the name of a section of a property is a duplicate, a warning symbol is added, which is fine.
- When accessing the duplicate name and exiting w/o edit, a second, additional warning symbol will be added, and the first warning symbol will be **added to the name and saved to the file**.
- When more than one section/property have an identical name, all will receive the same warning symbol, basically rendering them identical again.

A solution could be to add the warning symbol not to the actual name, but just as a visual queue and not allow a user to save an invalid odML file. See #58.

Start by reproducing the duplicate section/property-name flow described in this issue, including opening and exiting without editing, and review the related discussion in #58. Trace how warning symbols are applied and how the file-save path handles invalid odML names; done means warnings remain visual only and invalid files cannot be saved.

Written by the indexing model from the issue text.