Fix discounts

[dominik-zeglen]

I want to merge this change because it fixes sale dates and updates design.
Resolves #69

Pull Request Checklist

1. All visible strings are translated with proper context.
2. All data-formatting is locale-aware (dates, numbers, and so on).
3. Translated strings are extracted to .pot file.
4. Number of API calls is optimized.
5. The changes are tested.
6. Type definitions are up to date.
7. Changes are mentioned in the changelog.

[codecov]

Codecov Report

Merging #207 into master will increase coverage by 0.06%.
The diff coverage is 95.34%.

@@            Coverage Diff             @@
##           master     #207      +/-   ##
==========================================
+ Coverage    73.5%   73.57%   +0.06%     
==========================================
  Files         567      569       +2     
  Lines        5919     5942      +23     
  Branches     1007     1008       +1     
==========================================
+ Hits         4351     4372      +21     
  Misses       1394     1394              
- Partials      174      176       +2

Impacted Files	Coverage Δ
...ariantCreateDialog/ProductVariantCreateSummary.tsx	85.71% <ø> (ø)	⬆️
src/theme.ts	100% <ø> (ø)	⬆️
...mponents/VoucherDetailsPage/VoucherDetailsPage.tsx	71.42% <ø> (ø)	⬆️
...ounts/components/SaleCreatePage/SaleCreatePage.tsx	100% <ø> (ø)	⬆️
...nts/components/SaleDetailsPage/SaleDetailsPage.tsx	92.3% <100%> (+1%)	⬆️
src/discounts/components/SaleValue/SaleValue.tsx	100% <100%> (ø)
src/discounts/components/SaleType/SaleType.tsx	100% <100%> (ø)
...onents/VoucherRequirements/VoucherRequirements.tsx	88.88% <100%> (+1.38%)	⬆️
...VariantCreateDialog/ProductVariantCreatePrices.tsx	63.15% <100%> (ø)	⬆️
...discounts/components/VoucherValue/VoucherValue.tsx	90.9% <100%> (+5.19%)	⬆️
... and 6 more

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