Extending API to query required namespaces

[3dJan]

This PR adds a new API method to the model class that allows to query the namespaces required by extensions. This allows clients to decide weather the model can be loaded or not without any knowledge about future extensions, and without the need to parse the xml-file separately.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 64.50216% with 82 lines in your changes are missing coverage. Please review.

Project coverage is 69.17%. Comparing base (8ceec9c) to head (0f3ab86).

Files	Patch %	Lines
Autogenerated/Source/lib3mf_interfacewrapper.cpp	51.36%	71 Missing :warning:
Source/API/lib3mf_namespaceiterator.cpp	64.00%	9 Missing :warning:
Autogenerated/Bindings/Cpp/lib3mf_implicit.hpp	93.54%	2 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## develop #348 +/- ## =========================================== - Coverage 69.20% 69.17% -0.03% =========================================== Files 271 273 +2 Lines 28691 28922 +231 =========================================== + Hits 19855 20007 +152 - Misses 8836 8915 +79 ```

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