Improve API (API 1.1)

[krestenlaust]

#420 aims to document the API. This PR addresses inconsistencies found during that documentation effort. Both in implementation and in the actual API.

It increments the API versioning to 1.1

[krestenlaust]

QR-endpoint apparently uses Stregdollars as opposed to Stregøre. I feel like streamlining this is too big a change.
The QR-endpoint also takes a member parameter, which will probably be renamed to username to streamline with other Member API-methods. (member will probably still be supported)

[krestenlaust]

Changed response text on error to this format

[krestenlaust]

Changed response format for Active Products-endpoint:
{"1": {"name": "Test ØL", "price": 100}, "2": {"name": "Kold Kaffe", "price": 200}, "3": {"name": "Fadøl", "price": 1500}, "13": {"name": "Fake ØL", "price": 300}, "32": {"name": "Kold Kaffe", "price": 200}, "34": {"name": "Fnugfald", "price": 0}}

Instead of {"1": ["Test ØL", 100], ...}

[krestenlaust]

Changed format for Category_mapping endpoint output:
{"1": [], "2": [], "3": [], "13": [], "32": [[6, "kaffe"]], "33": [], "34": []} -> {"1": [], "2": [], "3": [], "13": [], "32": [{"category_id": 6, "category_name": "kaffe"}], "33": [], "34": []}

Much more verbose, but it's more like the other endpoints. Considering changing it to not return products which don't have any mapped categories

[krestenlaust]

I've decided to leave the sales API as is

[Mast3rwaf1z]

a few small changes, but looks nice 👍

[codecov]

Codecov Report

Attention: Patch coverage is 29.16667% with 34 lines in your changes missing coverage. Please review.

Project coverage is 80.63%. Comparing base (124ba7f) to head (3042946).
Report is 5 commits behind head on next.

Files with missing lines	Patch %	Lines
stregsystem/views.py	25.00%	30 Missing ⚠️
stregsystem/utils.py	42.85%	4 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             next     #421      +/-   ##
==========================================
- Coverage   80.82%   80.63%   -0.20%     
==========================================
  Files          40       40              
  Lines        3760     3774      +14     
  Branches      476      480       +4     
==========================================
+ Hits         3039     3043       +4     
- Misses        665      675      +10     
  Partials       56       56              

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[Mast3rwaf1z]

lgtm