On insights and project status, we would like to show "technica debt"
instead of "health". New value is that of `1/health`, or simplified:
`healthy flags / total flags`
This PR updates the tooltips for the health chart to also include
information on how healthy flags there are. The user could make this
calculation themselves before, but it'd require them to subtract the sum
of stale and potentially stale flags from the total. This makes it so
that they don't have to do the calculation.
I've also included a bar for the healthy flags in the overview, so that
it's easier to see how large a portion it is compared to the others.
Also: clean up some uses of the now-deprecated VFC.
