Add plotly as external dependency and clean up imports

content/js/meteorogram/meteorogram.js

content/js/meteorogram/meteorogram.js.map

content/js/meteorogram/package.json

content/js/meteorogram/plot/init.js

content/js/meteorogram/plot/ticks.js

content/js/meteorogram/plot/update.js

content/js/meteorogram/webpack.config.js

htdocs/aoss/tower/meteorogram/index.html

htdocs/data_download/index.html

htdocs/file_download/index.html

htdocs/js/data_download.js

htdocs/js/file_download.js

htdocs/js/form_util.js

htdocs/js/meteorogram/README

htdocs/js/meteorogram/controller.js

htdocs/js/meteorogram/dispatcher.js

htdocs/js/meteorogram/meteorogram.js

htdocs/js/meteorogram/meteorogram.js.map

htdocs/js/meteorogram/plot/data.js

htdocs/js/meteorogram/plot/init.js