vis.js: make cells narrower

As there is very little extra information within the cells health grid cells, they could be narrower and thus fit more information to the width of the screen.

For comparison, vis.js had approximately 25% narrower cells. It doesn't need to go that far, but little off would be nice.

Also, there was some discussion with Petri if the 'D' within the cells was necessary or not. @adrinael ?