mail: add members field for lists

we have to track the members of a list in the mail app separately
from groups. this is required because users can now have multiple
mailboxes. and because of that we cannot do a 1-1 mapping of group
members to mailboxes anymore. the ui is changed to select mailboxes
when creating a list.

migrations/schema.sql

@@ -167,6 +167,7 @@ CREATE TABLE IF NOT EXISTS mailboxes(
     ownerId VARCHAR(128) NOT NULL, /* app id or user id or group id */
     ownerType VARCHAR(16) NOT NULL, /* 'app' or 'user' or 'group' */
     aliasTarget VARCHAR(128), /* the target name type is an alias */
+    membersJson TEXT, /* members of a group */
     creationTime TIMESTAMP,
     domain VARCHAR(128),