fix: improve start behavior and logging, don't orphan react-scripts, add postcss

[amcgee]

This has one important functional change - we wait for the app build to succeed before starting the appShell server, so we don't run the risk of orphaning the server process if/when the first compilation fails (a fatal error in rollup). This also:

• Adds support for overriding the server port with the PORT env var
• Significantly improves the aesthetic appeal and consistency of console output
• Stops automatically piping the react-script output

[netlify]

Deploy preview for dhis2-app-platform ready!

Built with commit 5049038

https://deploy-preview-34--dhis2-app-platform.netlify.com

[amcgee]

Here's an example of what the output looks like when running start and encountering a few errors:

[varl]

The addition of postcss support makes this a feature bump.

I don't have the opportunity to try this tonight but will give it a whirl in the morning. Looks pretty slick!

[amcgee]

I was thinking about dropping postcss and adding it later, but figured since the compilation failed when it hit a CSS import before it could be considered a fix (doesn't change the API). Either way fine with me, we might want to do CSS imports differently in the future anyways.

The library in question that @erikarenhill was trying to use was @dhis2/analytics - this gets past the CSS import issue but there are other issues we'll need to deal with as well.

Taking out PostCSS for now

[varl]

Yeah, avoiding the css-loader situation was one of the reasons we rewrote ui-core from postcss to styled-jsx.

[varl]

Works on my machine. 👍

[amcgee]

Yeah, avoiding the css-loader situation was one of the reasons we rewrote ui-core from postcss to styled-jsx.

Yep, agreed. Libraries with styled-jsx should work, but we'll probably also have to at least temporarily support direct CSS imports (most notably for d2-ui)

I'll open another PR next week to address this and other issues importing some of our legacy libraries