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

* Implement a simplified version of the REFERENCES algorithm
* Remove FormatThreads function
* Instead of acting on all threads, handle each thread independently

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>

Configure an oauthbearer source without a token_endpoint
parameter would panic due to nil pointer dereference

  Example
    source=imaps+oauthbearer://frode.aa%40gmail.com@imap.gmail.com:993
    source-cred-cmd=pass oatuh2 frode.aa@gmail.com

token_endpoint is not required as it will use the provided
password as access_token when it is not set

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.