Avoid duplicated contacts after importing and enabling contact synchronization

[bedhub]

As an user I want to have just one instance of each contact inside my native address book after importing them and enabling contact synchronization inside Tuta app.

AC

• After importing and enabling synchronization there's just one local instance of the imported contacts
• There is only one contact container that we use for synchronisation, the sync container
• The sync container is the local container if present,  otherwise it is the default container.
• Warn users to disable iCloud sync if there's no local address book to prevent contacts from being synchronized between devices
• If user turns on contact synchronization we try to match the contacts in the sync container to prevent the unnecessary creation of contacts (iOS)

Tasks

• [ ] Add a warning about iCloud when enabling contact sync
• [ ] Add a check and warning about iCloud + contact sync after login
• [ ] Add a function to match existing contact with tuta contacts
• [ ] Take new match function into account to decide whether to create or update the contact

Notes

• Check what Gmail is doing. They are moving contacts to their own list.