Add accentColor props for iOS datetimepicker (#20)

[simartn]

Summary

This adds prop accentColor for iOS.
This relates to #20.

Test Plan

What's required for testing (prerequisites)?

Testing can be done with the example app. I added another input (accentColor) which can be used for testing.

What are the steps to reproduce (after prerequisites)?

Select display to compact or inline.
Enter a color value (i.e. #f00) into the accentColor field.
Check if picker appearance changes.

Compatibility

OS	Implemented
iOS	✅
Android	❌

Checklist

• I have tested this on a simulator
• I added the documentation in README.md
• I updated the typed files (TS and Flow)
• I added a sample use of the API in the example project (example/App.js)
• I have added automated tests, either in JS or e2e tests, as applicable

e2e test can not check color changes.

[peteratdivvy]

Would absolutely love for this to land. We really need a way to set the tintColor for the calendar.

[vonovak]

thank you for the PR!

it's looking good, we just need to get the e2e tests green. Let me know if you want to have a look or I can do it too 👍

[vonovak]

thanks a lot for the PR @simonnagl!

[vonovak]

Please let me know if you'd like to get more involved with the project and I can add you to the repo 🙂

[vonovak]

🎉 This issue has been resolved in version 6.1.0 🎉

If this package helps you, consider sponsoring us! 🚀

[simartn]

@vonovak Thank you a lot for maintaining this repo! And for the quick an gentle code review.

I may create further pull requests if needed personally. I likely will not work on the project on a open issue basis.