Avoid sending the "from" JID before starttls

[realbiz21]

Is your feature request related to a problem? Please describe.
No, but it would increase user privacy.

When establishing an initial connection to an XMPP server, the following is sent without encryption when a client executes the XmppClient.login() method:

<stream to="[server]" from="[user_jid]" ...>

The user's JID is exposed prior to the starttls proceeding and visible to a passive network observer.

Describe the solution you'd like
Restrict sending of from="[user_jid]" before starttls has occurred. This issue was originally raised at tigase/Martin#22 and a potential solution is already known:

let client: XMPPClient;
client.connectionConfiguration.useSeeOtherHost = false

Describe alternatives you've considered
N/A

Additional context
Using: Siskin IM 7.3.3