Parents are not imported when importing a vcard

[rezbyte]

Bug in mobile app

Describe the bug
A clear and concise description of what the bug is.

To Reproduce
Steps to reproduce the behavior:

1. Create a contact with a 'parent' relation in Android's included contact app
2. Export the contact as a vcard
3. Import the vcard into Tuta Mail's contacts
4. See the parent is missing

Expected behavior
The imported contact has a relation 'Parent'.

Smartphone (please complete the following information):

• OS: Android

[murilopereirame]

Google uses a custom field to export relations on vCards and it doesn't comply with the RFC so we should close this issue as we do not support custom fields for now.