Bug: Undo undoes multiple changes despite pauses between them

[moeffju]

This might just be due to an automatic edit run merge or something, but:

• Open a completed job in the transcribee editor
• Edit some word
• Wait for a few seconds
• Then jump to another word by clicking a word or selecting a substring and quickly start typing
• Hit undo

Actual:

• Your recent typing and your previous edit are undone

Expected:

• Undo should undo only the last edit. Repositioning the cursor or pausing editing for a certain amount of time should result in a separate transformation event to be undone.