This requires another database schema change. With this change messages
at the root of a thread reference themselves in the 'threads' table,
i.e. 'root' contains the value of 'id' for these messages. It makes
selecting all messages in a thread much simpler.
Database updates can be surprisingly slow. This lead to slow updates of
the user interface which in turn made working with K-9 Mail not as fun
as it should be. This commit hopefully changes that.
- show thread as starred if at least one message in it is starred
- use arrival date of last message as thread arrival date
- use sum of message attachment counts in thread as thread attachment
count
- show thread as answered/forwarded if all messages in thread were
answered/forwarded
Currently only the Accounts activity uses the new count.
While working on this I realized that the unread/flagged search for
accounts currently looks for unread/flagged messages in all folders, not
all displayable folders without special folders (Trash, Spam, Outbox,
Sent, Drafts) like we used to.
Also, the "All messages" search currently doesn't limit the search to
searchable folders like it is supposed to.