Add ability to move blocks by drag-n-drop - [ ] should work with one block and with several selected blocks - [ ] Should use same scroll behaviour as used in RectangleSelection - [ ] Should work by pressing on Block Tunes toggle (and alt-text should be `Click to tune or drag to move`) <img width="237" alt="image" src="https://user-images.githubusercontent.com/3684889/152971766-115dd4f5-41b1-478b-8c6a-f8701d400303.png">