Editor: side-by-side view

[neos-bot]

Jira issue originally created by user daniel:

In order to translate content elements of a document, the editor wants to see a side-by-side view (split screen) of the original content and translated content. The editor may choose to defer from a 1-1 translation and remove specific elements in the second language version or add content elements which don't exist in the original language. The side-by-side view will show which content elements correlate with others in the respective language.

Jira-URL: https://jira.neos.io/browse/NEOS-631