Sensors attached to model runs and more backend tests

[mhauru]

Adds tests for all the backend API endpoints that were missing them, and finishes the work on the endpoints related to inserting and getting information about sensors and sensor measures associated with model runs. In the process, fix various small things in the files I was editing.

Builds on #165, so merging that first will make the diff for this shorter.

Closes #126 and #41

[codecov-commenter]

Codecov Report

Attention: 20 lines in your changes are missing coverage. Please review.

Comparison is base (7e2fba7) 86.69% compared to head (9b7c6f0) 87.71%.

:exclamation: Current head 9b7c6f0 differs from pull request most recent head 528960e. Consider uploading reports for the commit 528960e to get more accurate results

Files	Patch %	Lines
dtbase/backend/api/location/routes.py	80.76%	5 Missing :warning:
dtbase/core/models.py	83.87%	5 Missing :warning:
dtbase/webapp/app/locations/routes.py	71.42%	4 Missing :warning:
dtbase/core/locations.py	72.72%	3 Missing :warning:
dtbase/backend/api/model/routes.py	80.00%	2 Missing :warning:
dtbase/tests/test_api_models.py	98.75%	1 Missing :warning:

Additional details and impacted files

```diff @@ Coverage Diff @@ ## main #168 +/- ## ========================================== + Coverage 86.69% 87.71% +1.01% ========================================== Files 70 71 +1 Lines 4759 4923 +164 ========================================== + Hits 4126 4318 +192 + Misses 633 605 -28 ```

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[EdwinB12]

Specific features implemented in this PR:

1. Add Documentation for multiple endpoints:

• get-schema-details
• get-model-run-sensor-measure
• get-model-run

2. Add API json details to docstrings of routes.