In order to allow importing of mails we replace legacy MailFolders
(non-static mail listIds) with new MailSets (static mail listIds).
From now on, mails have static mail listIds and static mail elementIds.
To move mails between new MailSets we introduce MailSetEntries
("entries" property on a MailSet), which are index entries sorted by
the received date of the referenced mails (customId). This commit adds
support for new MailSets, while still supporting legacy MailFolders
(mail lists) to support migrating gradually.
* TutanotaModelV74 adds:
* MailSet support
* and defaultAlarmList on GroupSettings
* SystemModelV107 adds model changes for counter (unread mails) updates
* Adapt mail list to show MailSet and legacy mails
The list model is now largely unaware about listIds since it can
display mails from multiple MailBags. MailBags are static mailLists
from which a mail is only removed from when the mail is permanently
deleted.
* Adapt offline storage for mail sets
Offline storage gained the ability to provide cached entities
from a list of ids.
