Feature/rollup

[gijsroge]

Still in draft, please refrain from reviewing WIP.

This pull request introduces Rollup to allow for bundling of JavaScript.

• This allows you to import first/third party modules from any JavaScript file.
• Allows us to easily integrate features like; TypeScript, outputing manifests, dynamic imports (for lazy loading modules).

Breaking changes:

• JavaScript outputs is always scoped, never global
• Same counts for the concatenated files
• Outputs a flat structure. If the source file is in sub/sub/sub/a.js it outputs -> dist/js

Progress:

• Documentation
• Check if https://github.com/rollup/stream could simplify the integration.. 😅
• Support gulp watch
• Add Rollup bundling
• Update tests

[MartijnCuppens]

Do we even need js-concat, since we can now merge the files with the import (can we, not sure?)?

We can't keep

buildozer/lib/.buildozerrc

Lines 21 to 23 in 12484be

	js:
	- src: js/**/*.js
	dest: dist/js

since this will generate a separate js file for each js file. Thoughts on changing this to:

js:
  - src: js/**/index.js
    dest: dist/js

[gijsroge]

Small follow up. Did not have much time last couple of months. Planning on picking this back up soon.