feat: Move purchase-heatmap category definitions to config file

[ha36d]

resolves #375

[codecov]

Codecov Report

❗ No coverage uploaded for pull request base (next@5d6d103). Click here to learn what that means.
The diff coverage is 100.00%.

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@@           Coverage Diff           @@
##             next     #379   +/-   ##
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  Coverage        ?   53.90%           
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  Files           ?       33           
  Lines           ?     4512           
  Branches        ?      265           
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  Hits            ?     2432           
  Misses          ?     2030           
  Partials        ?       50           

Files	Coverage Δ
stregsystem/purchase_heatmap.py	57.21% <100.00%> (ø)
treo/settings.py	32.86% <100.00%> (ø)

[krestenlaust]

The issue has been updated to a more fitting solution. As opposed to storing it in a config file, it should be configurable in the admin panel. Sorry about the change of mind.