Copy/Paste on top of selected blocks adds rather than places

[alexzrh]

• Have some blocks/code in the editor
• copy code from another place (slack, for example)
• Do command-a (mac) in QS to select all the blocks/code
• Do command-v (mac) to paste all the code from the clipboard into QS

actual outcome: Code pasted in is added to the existing QS code expected outcome: code in QS should be replaced