tools: Put clipPath in defs to placate Inkscape
tools: Only render stripes inside clipPath

Previously, this also rendered the fill for 100% regions in the
clipPath, which is redundant and makes it more difficult to work with
in Inkscape.
tools: Control over heat map separators
tools: Control over heat map key labels
tools: Control over global SVG CSS properties

This is useful, for example, to control the font.