Add valid until date

[Roshyo]

Fixes #169

• [x] Tests (unit/spec)
• [x] Danish translations
• [x] Validator for default period in admin

[codecov[bot]]

Codecov Report

Merging #177 (d3c44ef) into 0.12.x (92cbf10) will increase coverage by 2.14%. The diff coverage is 73.41%.

@@             Coverage Diff              @@
##             0.12.x     #177      +/-   ##
============================================
+ Coverage     39.71%   41.85%   +2.14%     
- Complexity      457      483      +26     
============================================
  Files            88       92       +4     
  Lines          1483     1560      +77     
============================================
+ Hits            589      653      +64     
- Misses          894      907      +13     

Impacted Files	Coverage Δ
src/Form/Type/GiftCardConfigurationType.php	0.00% <0.00%> (ø)
src/Form/Type/GiftCardType.php	0.00% <0.00%> (ø)
...ator/Constraints/GiftCardIsNotExpiredValidator.php	87.50% <87.50%> (ø)
src/Form/Type/DatePeriodType.php	90.90% <90.90%> (ø)
src/Validator/Constraints/DatePeriodValidator.php	92.30% <92.30%> (ø)
src/Factory/GiftCardFactory.php	100.00% <100.00%> (ø)
src/Model/GiftCard.php	74.52% <100.00%> (+2.94%)	:arrow_up:
src/Model/GiftCardConfiguration.php	81.25% <100.00%> (+14.58%)	:arrow_up:
src/Provider/DatePeriodUnitProvider.php	100.00% <100.00%> (ø)

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[loevgaard]

Can you add some screenshots of the changes in admin?

[Roshyo]

@loevgaard added one new translation, please update "da" file