:sparkles: [#69] added categorie endpoint and atribute on partij

[bart-maykin]

fixes #69

• added model categorie
• added categorie in admin
• added categorie api endpoint
• added categorie as inline field on the partij serializer
• added tests for categorie api endpoint

[codecov-commenter]

Codecov Report

Attention: 10 lines in your changes are missing coverage. Please review.

Comparison is base (a41b96e) 97.01% compared to head (408642c) 97.05%.

Files	Patch %	Lines
...ant/components/klantinteracties/models/partijen.py	73.91%	6 Missing :warning:
...ponents/klantinteracties/api/filterset/partijen.py	91.11%	4 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #139 +/- ## ========================================== + Coverage 97.01% 97.05% +0.03% ========================================== Files 179 180 +1 Lines 7508 7940 +432 ========================================== + Hits 7284 7706 +422 - Misses 224 234 +10 ```

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