Fix bug with Google Visualization plugin.
 * Didn't want to make local changes to plugin, as described in:
   * http://stackoverflow.com/questions/24776975/google-visualization-api-graphs-are-not-displaying-in-gsp-pages
 * Settled for changing per-plugin encoding, as described in:
   * https://github.com/bmuschko/grails-google-visualization/issues/28
   * https://jira.grails.org/browse/GPGOOGLEVISUALIZATIONAPI-14