#12 Unique ids for sub-entities not unique

[Aleksander Vines]

Currently, unique ids for sub-entities (f.ex. entities in lists) are generated as a random number between 0 and 1000000. There is a small chance of id collision, which would result in unexpected behavior, such as only being able to change content of the first sub-entity with that UID.
This UID is currently generated in DocumentEditor?.