Signed-off-by: Kevin Kuehler <keur@xcf.berkeley.edu>

* Import the go-imap-sortthread library
* Add sortthread client to imapClient in worker
* Add handleDirectoryThreaded, which uses the go-imap-sortthread, and
  converts the results to the aerc thread type

Signed-off-by: Kevin Kuehler <keur@xcf.berkeley.edu>

This changes the search flags for maildir and imap backends.

They now no longer use -t for searching all text. This seems to make
more sense as being the targeted recipient. I have similarly added Cc
for -c. The text search now resides under -a for all text.

This patch adds search behaviour to allow searching in the body of the
messages, the entire text (body + header), and searching just the from
header.

Signed-off-by: Wagner Riffel <wgrriffel@gmail.com>

This fixes ~sircmpwn/aerc2#245. This sets up the imap client to send
error messages to the logger of the worker. Errors now end up in the
bottom status line.

https://todo.sr.ht/~sircmpwn/aerc2/245

This allows backends which can't always be compiled due to missing
dependencies (say libnotmuch) to be compiled conditionally with buildflags.

    imaps+oauthbearer://user:token@host?token_endpoint=...

 - the config Source password is used as access token if
   no token_endpoint parameter is set
 - the config Source password is used as refresh token if
   token_endpoint parameter is set, and used to exchange
   with an access token

The implementation has only been tested with Gmail.

    source = imaps+oauthbearer://{username}:{refersh_token}@imap.gmail.com:993? \
    client_id=XX&\
    client_secret=XX&\
    token_endpoint=https%3A%2F%2Faccounts.google.com%2Fo%2Foauth2%2Ftoken

client credentials created with

    https://console.developers.google.com/apis/credentials

refresh token created with

    https://github.com/google/gmail-oauth2-tools/blob/master/python/oauth2.py

rel: https://todo.sr.ht/~sircmpwn/aerc2/42