Move from templateData.htmlmin to plugins.htmlmin

[RobLoach]

  templateData:
    htmlmin:
      removeComments: true
      removeCommentsFromCDATA: false
      removeCDATASectionsFromCDATA: false
      collapseWhitespace: true
      collapseBooleanAttributes: false
      removeAttributeQuotes: false
      removeRedundantAttributes: false
      useShortDoctype: false
      removeEmptyAttributes: false
      removeOptionalTags: false
      removeEmptyElements: false

The above should likely move to plugins.htmlmin to match other plugin configuration options:
https://github.com/docpad/docpad-plugin-stylus/#defaults