[GSoC 22] [undo] Add 'undo' for the single latest copy operation

[WIP] MR to add the ability to 'undo' the single latest copy operation performed. (#819 (closed) and #191 (closed)).

TODO

Phase 1

• Learn more about ThunarJob
• Write ThunarJobOperation
  • Basic struct
  • Operation type as property
  • Source and target file lists as properties
  • Switch to operation-kind as an enum
• Write persistent global operation GList, ThunarJobOperationList
• Register latest copy on global ThunarJobOperationList

Phase 2

• Write function to calculate inverse ThunarJobOperation for copy
• Write undo to execute the inverse of the latest ThunarJobOperation
• Write keybindings and front-end buttons for undo