Add 'dev' script to do a development build

[vojtechszocs]

Addressing comment #150 (comment)

• add dev script to do a development build (one-time) without any pre-checks
• ensure that regular production build (build script) has NODE_ENV set accordingly
• updated developer guideline

Q: why not use --watch for the dev script?
A: our build is split into two parts, JS and Sass. JS files are processed by Babel, Sass files are copied as-is. While Babel supports --copy-files to include files that weren't part of the JS compilation, this would require changing --out-dir and transforming file paths, for which I didn't find any suitable Babel plugin. We could use webpack and its watch mode on top of Babel, but I'm reluctant to add such complexity for now.

Q: is there actually a difference between production and development build?
A: not right now 😃 it seems like NODE_ENV has no effect on our build outputs at the moment:

$ yarn build && mv dist dist_prod
$ yarn dev && mv dist dist_dev
$ diff -r dist_prod dist_dev # no results

[coveralls]

Pull Request Test Coverage Report for Build 481

• 0 of 0 changed or added relevant lines in 0 files are covered.
• No unchanged relevant lines lost coverage.
• Overall coverage remained the same at 87.749%

---

Totals
Change from base Build 479:	0.0%
Covered Lines:	1647
Relevant Lines:	1796

---

💛 - Coveralls

[atiratree]

thanks!

[atiratree]

Watch mode would be nice to have though. Mainly because web-ui dev watch mode breaks when we delete our dist. Then, web-ui dev needs to be restarted.

web-ui dev output:

ERROR in ./public/style.scss
Module build failed (from ./node_modules/mini-css-extract-plugin/dist/loader.js):
ModuleBuildError: Module build failed (from ./node_modules/thread-loader/dist/cjs.js):
Thread Loader (Worker 9)

ERROR in ..-components/dist/js/index.js
Module build failed (from ./node_modules/thread-loader/dist/cjs.js):
Thread Loader (Worker 8)
ENOENT: no such file or directory, open '$AT_LOCATION/kube-web-ui-components/dist/js/index.js'