Preparation for a sortable mailbox. Otherwise the model would resort
itself and select mail again forever.
Arrow keys will no longer load mail automatically, now you also need to
hit Enter.
This lets us bubble up errors from `LibIMAP::Client::send_command()`,
which can happen if the connection hangs or is taking a long time, and
the user closes Mail.
Also moves WebContentClient and the references to the generated IPC
descriptions, since they are all components of OutOfProcessWebView.
This patch has no functional changes.
This utilises LibIMAP and LibWeb to provide an e-mail client.
The only way currently to connect to a server and login is with a
config file. This config file should be stored in ~/.config/Mail.ini
Here is an example config file:
```
[Connection]
Server=email.example.com
Port=993
TLS=true
[User]
Username=test@example.com
Password=Example!1
```
Since this is stored in plaintext and uses a less secure login method,
I'd recommend not using this on your main accounts :^)
This has been tested on Gmail and Outlook. For Gmail, you either have
to generate an app password if you have 2FA enabled, or enable access
from less secure apps in your account settings.
