Updates to the holidays of Croatia, starting from the year 2020

[krukru]

Starting from the year 2020, there are some changes to the national holidays of Croatia. Some holidays have changed names, some have been disbanded and a new holiday was added.
The holiday list which is valid from the year 2020 can be found at the "Narodne novine" https://narodne-novine.nn.hr/clanci/sluzbeni/2019_11_110_2212.html
(English: The People's Newspaper), the official gazette of the Republic of Croatia which publishes laws, regulations, appointments and official decisions and releases them in the public domain

Edit: The full list of changes

• Statehood day is now celebrated at a new date. The old date is still remembered (called "Spomendan") as Independence Day (Dan neovisnosti), but is not an official holiday.
• Homeland Thanksgiving Day has been given a different name to include Victory Day and Day of Croatian Defenders (full name: Dan pobjede i domovinske zahvalnosti i Dan hrvatskih branitelja/Victory and Homeland Thanksgiving Day and the Day of Croatian Defenders).
• Independence Day is no longer an official holiday. (It is still remembered as a "Spomendan" and is called Croatian Parliament Day. This PR only removes the official holiday - does not add the "Spomendan").
• A new official holiday is created called "Remembrance Day for Homeland War Victims and Remembrance Day for the Victims of Vukovar and Skabrnja"

[stelgenhof]

Thanks for this PR! Everything looks good, only can you update the CHANGELOG.md file describing these changes (add it in the 'Unreleased' section). Cheers!

[krukru]

Hey @stelgenhof, I briefly updated the changelog and updated the PR description to include full list of changes.