metadata-indicator: show key and value on hover
metadata-indicator: show key and value on hover

Fix #455.

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