add possibility for nested loaders

[justusschock]

What does this PR do?

Extends #1959 to the possibility of nested loaders as mentioned by @tchaton in #1959 (comment)

PR review

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Ps: Sorry for the formatting, this happens automatically on import in my IDE. Hope this isn't an issue in this small PR.

[pep8speaks]

Hello @justusschock! Thanks for updating this PR.

There are currently no PEP 8 issues detected in this Pull Request. Cheers! 🍻

Comment last updated at 2021-01-24 10:45:49 UTC

[codecov]

Codecov Report

Merging #5404 (baee078) into release/1.2-dev (6386f45) will decrease coverage by 0%.
The diff coverage is 94%.

@@               Coverage Diff               @@
##           release/1.2-dev   #5404   +/-   ##
===============================================
- Coverage               92%     92%   -0%     
===============================================
  Files                  153     153           
  Lines                10834   10840    +6     
===============================================
  Hits                 10011   10011           
- Misses                 823     829    +6     

[Borda]

lgtm

[tchaton]

Great !