add Ctrl+S key binding in slice editor
add Ctrl+S key binding in slice editor

Fix #1264

aumayr/beancount-web,beancount/fava,yagebu/fava,yagebu/fava,beancount/fava,yagebu/fava,aumayr/beancount-web,beancount/fava,beancount/fava,beancount/fava,aumayr/beancount-web,yagebu/fava,yagebu/fava,aumayr/beancount-web