webpack works well with vizmake process

[lindsayplatt]

PR #6 makes everything happen, BUT you have to run unpublish() and then vizmake() to get webpack to re-bundle the js modules if you edit anything since they are not a target.

We could...

1. make every js module a target in viz.yaml and have the bundle publish step depend on each one.
2. re-run the webpack bundle step every time vizmake is called no matter what
3. work webpack into vizmake function

Potential things for number 3:

parameters:
  -
    id: webpack_input_js
    location: src/app.js
  -
    id: webpack_output_js
    location: bundle.js
  -
    id: webpack_module_dir
    dir: src/modules/
...

publish:
  - 
    id: js_bundle # get appropriate script tag
    relpath: ??????
    mimetype: application/javascript
    depends: webpack_output_js
  -
    id: figure_section # need this so that d3 code gets run after d3 has been loaded
    template: layout/templates/main_fig.mustache
    publisher: section
    depends:
      script: js_bundle
    context: 
      script: script
  -
    id: webpack_config
    template: webpack_config.mustache
    publisher: ??????
    depends:
    	input: webpack_input_js
	output: webpack_output_js
	context:
		input: input
		output: output

---------- webpack_config.mustache ----------

const webpack = require("webpack");

module.exports = {
    entry: './{{input}}',
    output: {
        filename: './{{output}}'
    },
    plugins: [
      new webpack.ProvidePlugin({
          d3: 'd3'
      })
    ]
};

---------- vizmake() calls a function called webpacker() ----------

check to see if package.json existed. if not, run `npm init -y`
check to see if correct node_modules are installed. if not install them.
check to make sure webpack.config.js exists (throw error if it doesn't because that should come from publish step)
?? when does package-lock.json get created?

once everything else is published `npm run start`

[lindsayplatt]

Right now this is functioning as I would expect with vizlab v0.3.8 or greater. Specific things can be created as new issues.