bake/serve: Fix how taxonomy index pages are setup and rendered. * Properly use the taxonomy's setting name where appropriate. * Delete duplicated (and sometimes incorrect) code in 2 places to setup filtering on an index page and consolidate it on the `PageRenderingContext`. * Add unit tests.

{
  "name": "PieCrust",
  "version": "0.0.1",
  "private": "true",
  "dependencies": {
    "bootstrap": "~3.3.2"
  }
}