Fixes Undo/Redo

[clicketyclackety]

Description

This PR fixes any issues with Undo/Redo, even for release and any other commands.

Fixed Undo / Redo.

• Added an UnDelete event to capture undo.
• Removed Guid for new speck. This prevents specks with duplicate IDs. Now Specks are always unique.

Tests

• [x] Create a new element, move it, undo and redo that
• [x] Release elements, and then undo/redo that. This works quite nicely, even with many items released. On the creators machine the undo deletes elements from others (like delete does) Redo re-adds the elements, but they will need releasing again. This does also even delete items that are selected by other users. Something to look at

Type of change

Please delete options that are not relevant.

• [x] Bug fix (non-breaking change which fixes an issue)

[karimi]

This is actually pretty intuitive in most cases! Well done!

Consider the scenario below:

1. User A: creates a circle
2. User A: moves circle from (0,0,0) to (1,1,1)
3. User A: releases
4. User B: deletes the circle
5. User A: undo
6. Circle reappears in (0,0,0)

I don't have a good answer for what should happen, but I find step 6 a bit confusing. Aside from leaving it as is, I can imagine it working a few different ways:

• Every time you release, your undo stack gets reset. So in the example above after User A releases, they can't go back and undo anymore
• Or, Undo should pay attention to objectID and only proceed if user performing the undo was the last person touching that object. In the example above, let's say user A before creating the circle draws a line. The circle created by User A has ID: 001 , when User A tries to undo, we do a check and see first undo step affects ID: 001 and last player on that ID was a different user. Therefore this step gets skipped. But next step in undo stack is the line with an ID that was last touched by the same user, so we proceed with undo.

Anyway, sorry for the wall of text. I think we should definitely merge this PR as is but think about these scenarios a bit more.