feat(build): change import for barrel file's, update seed doc

[nouc23]

fixes #1912

PR Checklist

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• read and followed the CONTRIBUTING.md guide.
• built and tested the changes locally.
• added/updated tests.
• added/updated API documentation.
• added/updated demos.

[codecov]

Codecov Report

Merging #2990 into development will decrease coverage by 1.03%.
The diff coverage is 100%.

@@               Coverage Diff               @@
##           development    #2990      +/-   ##
===============================================
- Coverage        65.03%   63.99%   -1.04%     
===============================================
  Files              210      207       -3     
  Lines             5691     5597      -94     
  Branches          1000      985      -15     
===============================================
- Hits              3701     3582     -119     
+ Misses            1724     1669      -55     
- Partials           266      346      +80

Impacted Files	Coverage Δ
src/component-loader/component-loader.class.ts	74.5% <ø> (-0.33%)	⬇️
src/modal/modal.module.ts	90.9% <100%> (ø)	⬆️
src/tooltip/tooltip.directive.ts	56.7% <100%> (-4.13%)	⬇️
src/popover/popover.module.ts	100% <100%> (ø)	⬆️
src/index.ts	100% <100%> (ø)	⬆️
src/dropdown/bs-dropdown.module.ts	92.85% <100%> (ø)	⬆️
src/component-loader/component-loader.factory.ts	66.66% <100%> (-33.34%)	⬇️
src/progressbar/progressbar.component.ts	93.75% <100%> (ø)	⬆️
src/popover/popover.directive.ts	78.57% <100%> (-3.58%)	⬇️
src/tooltip/tooltip.module.ts	100% <100%> (ø)	⬆️
... and 58 more

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[valorkin]

FYI we found couple more issues with systemjs, fixing...

[valorkin]

@IlyaSurmay how to make angular-cli fail on build if imported not from index file
?disable node module resolution?

[valorkin]

thanks for contribution :)