Remove title which displays number of participations
Replace fixed gray color with transparent highlight on hover
Hide text which overflows cell width
Replace magic numbers with constants
Display the name of the child cells in title (tooltip shown on hover)
Remove commented out code for rect.parent and associated CSS
Set grandparent in neutral colors: white on black, gray on hover
Use '>' instead of '.' as separator in breadcrumbs
Jump intermediate levels, which will only be displayed with colors
Scale cell width to measure whether text fits
Remove line of commented out code
Compute expected width/height using same function for text and rect
Update text visibility at the same time as text position

There is no need, with the right computation of the expected
width and height, to update the text visibility at a later time.