Undo functionality and load graph button

[VictorSolal]

To test, in conjunction with the pull request in the submodule:

• hit play
• open realityflow window
• log in
• create a new project
• create a new visual scripting graph
• load the graph on the whiteboard. Make sure you only have to click the button once!
• add 2 new float nodes
• add a new float parameter
• connect edges between all 3
• delete the middle one
• hit undo and see what happens
• hit clear graph
• hit undo
• hit create graph
• hit undo
• do any further undo testing you think is necessary (there are a lot of possible thorough tests)