minor usability improvements: links, jumpiness

- make notice header height static
  so that overall page height doesn't jump around

- make links convert from href to Router.navigate
  on the fly, which allows opening in new tab/window/etc
  and allows browser to print link dest, which is useful

- graph color assignments are more stable
  LRU cache of 31 label -> color assignments
bump the version to 2.0-beta19