Birthday with "Hide year" enabled in a contact does not include in the exported vcf file

[Guru-25]

To reproduce:

1. Add any date in Birthday field in a contact with "Hide year" option enabled.
2. export the .vcf file and open it with a text editor, BDAY column will be empty

Version: 6.15.0 Pro (Installed from Github releases)

[qwertyfinger]

@tibbi This is caused by PartialDate being only supported in vCard v4.0. But not all other apps support this version. For example, Google's default Contact app doesn't. So we have 2 options:

1. Export partial dates inside v4.0 vCard version, but then some other apps will display the date as "--mmdd".
2. Export partial dates inside v3.0 vCard version as usual dates but with the year 1900.

Simple Contacts will handle import correctly in any case.

Of course, we can give user the option to choose between export versions but that would complicate UX.

Here you can see the difference after importing the .vcf file in Google Contacts:

1. vCard v.4.0
2. vCard v.3.0

[tibbi]

we use version 3, so lets make it 1900 then

[qwertyfinger]

For more clarity:

1. v3 approach: https://github.com/SimpleMobileTools/Simple-Contacts/compare/master...qwertyfinger:partial-date-export-v3
2. v4 approach: https://github.com/SimpleMobileTools/Simple-Contacts/compare/master...qwertyfinger:partial-date-export-v4

[tibbi]

If we want to switch to v4, we have to do proper testing of every single field. You cannot just toggle it like this and hope that nothing will break. Lets stick to v3 for now.