Undo only undos added gradients

[vicmeow]

Describe the bug
The undo button undos only the addition of a gradient. A user should also be able to undo the deletion of a gradient.

To Reproduce
Steps to reproduce the behavior:

1. Add a gradient by clicking “add”
2. Delete the added gradient by clicking “delete”
3. Click “undo” to undo the deletion
4. See error, only undos the adding of a gradient

Expected behavior
Should undo the latest action, not just the add action

Screenshots
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Desktop (please complete the following information):

• OS: [e.g. iOS]
• Browser [e.g. chrome, safari]
• Version [e.g. 22]

Smartphone (please complete the following information):

• Device: [e.g. iPhone6]
• OS: [e.g. iOS8.1]
• Browser [e.g. stock browser, safari]
• Version [e.g. 22]

Additional context
Add any other context about the problem here.