Refs #14607; Styles(eunis.css) added lower risk threat levels

- Added lower risk threat level with the abbreviations described at
  http://en.wikipedia.org/wiki/IUCN_Red_List ( lr-cd, lr-nt, lr-lc )
- Added foreground and background colors for these threats with the colors
  found in the svg file attached in the wikipedia article.
  These are prefixed with wk indicator for ex: threat-level-nt-wk