Re: [pgAdmin4]: Webpacking of static JS/CSS

Hi

While this patch is in review, i have not attached patch for "unvendored libs" which is around 10MB in size and needs not to review.

Attached is the patch which can be reviewed.

Changes:

1) As React will be used in other modules, so the React components codebase is bundled into "vendor.js". the sqleditor.js bundle size is now just 239kb(excluding react)

If a module needs React package as dependency, the user can write:

`import React from 'react' or

`require('react')`

in respective module.

2) As Matt earlier pointed, application takes longer to start while generating bundle files. I used "hard-source-webpack-plugin" to reduce the build time and couple of other optimisations.

- Initially webpack build time: 25.13 seconds

- After removing 'pgadmin/browser' from ' resolve > modules, the time taken to build is reduced to 24.74 seconds

​- ​

After downgrading css-loader@0.28.0 to css-loader@0.14.0

​, it took 22.44 seconds.

​The older version of css-loader doesn't have other  packages like 'post-css', so it doesn't take much time to build.

While "hard-source-webpack-plugin" manages the cache and stores it into 'generated/.cache/<env><hash>/' path.​ So when the build is run  for the first time, it takes ~22 seconds.`

When run for second time, it takes 2-3 seconds to build. it builds only the chunks which have changes.

When build in production mode, initially it took ~47 seconds.

On second run, it took ~22 seconds. the only change between development and production builds are "CommonChunks" and "UglifyJS" plugins which are used for production build. So, "hard-source-webpack-plugin" doesn't seems to support build with these two optimisation plugins.

Please review updated patch.