renamed attachment's parentId to more fitting ownerId

db/migrations/0219__attachments.sql

@@ -1,7 +1,7 @@
 CREATE TABLE IF NOT EXISTS "attachments"
 (
     attachmentId      TEXT not null primary key,
-    parentId       TEXT not null,
+    ownerId       TEXT not null,
     role         TEXT not null,
     mime         TEXT not null,
     title         TEXT not null,
@@ -14,8 +14,8 @@ CREATE TABLE IF NOT EXISTS "attachments"
     isDeleted    INT  not null,
     deleteId    TEXT DEFAULT NULL);
 
-CREATE INDEX IDX_attachments_parentId_role
-    on attachments (parentId, role);
+CREATE INDEX IDX_attachments_ownerId_role
+    on attachments (ownerId, role);
 
 CREATE INDEX IDX_attachments_utcDateScheduledForErasureSince
     on attachments (utcDateScheduledForErasureSince);