Deal as well with sending key if key is outdated in the providers nicknym.

- Resolves: #8819, #8832

I've removed the add_listener method because it's not used anywhere.

When setting the listeners in the IMAP Folder, we avoid setting more
than one listener for the same imap mailbox (because in some situations
we were registering way too many listeners).

this was making the pixelated inbox registering the notification and
therefore the imap mailbox not being registered.

this MR also refactors the way pixelated is initialized, so that it
avoid creating a second Account instance. In this way, we make sure that
the pixelated mua and the imap server share the same collections for a
given mailbox, and therefore any of the two is able to get a
notification whenever the other adds a message to the mailbox.

- Resolves: #8846, #8798

mock a renamed method.

In addition to the UnicodeError exception in _process_decrypted_doc
function, we have added ValueError to the exception list so that we can
catch any error in JSON parsing, specially a 'NODATA' error that we were
getting with some of the emails.

This is in reference to issues -
https://github.com/pixelated/pixelated-user-agent/issues/908 &
https://github.com/pixelated/pixelated-user-agent/issues/981 - to ignore
documents that have this problem and not have Soledad try to sync them
again and again.

with @deniscostadsc

with @deniscostadsc

- some pep8 problems
- some confusion with old and new code after merging
from old keymanager

Before we used to have content_doc.content_type = 'text/plain;
charset="utf-8"'.
Currently, we have content_doc.content_type = 'text/plain'.

This change will give us, on top of that: content_doc.charset = 'utf-8'.
One can reconstruct the original one using .content_type and .charset.