make all notifications disappear after 5 seconds
make all notifications disappear after 5 seconds

Close #658

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