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)