QTFred event editor improvement: 'new event from paste' function

I would have this on right click, possibly also a shorter shortcut from having a valid expression selected... this would be just like clicking new event and then pasting an expression into it, but all in one action.

ideally if a paste is valid as the root this would make it the root, and if it's valid as either of the leaves of a default event it would make an event with the expression pasted into where it's valid.