Fix source editor bugs
Fix source editor bugs

- Double submission of forms
- Line highlighting

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