Implement "Send to back/front"

[pobch]

Need this feature for an image

TODOs

Separate the following tasks into multiple PRs.

• [x] When finding a single element by mouse position, start finding it from the last index instead of the first index.
• [x] Use timestamp to generate each element id instead of using the index number
• [x] There should be no removed element anymore. Instead, actually remove it from the array.
• [ ] Send to back = store that element, splice to remove the element from an array, put the stored element to the first index by unshift.
  • Create a new mode: "moveElementsToFirstIndex" for commitNewSnapshot() inside useHistory()
• [ ] Send to front = store that element, splice to remove the element from an array, then push the stored element into the array.
  • New mode "moveElementsToLastIndex"