https://xmpp.org/extensions/xep-0198.html#resumption
The <resume/> element MUST include a 'previd' attribute whose value
is the SM-ID of the former stream and MUST include an 'h' attribute
that identifies the sequence number of the last handled stanza sent
over the former stream from the server to the client.
- Set roster_fetched flag when we get an empty IQ[type="result"] stanza
- Set `restored` flag when resuming in converse-smacks
- Don't trigger change event when fetching xmppstatus values
- Removed two events, since we can just listen to `change` on `_converse.xmppstatus`.
- Remove the `keepalive` configuration setting. It is now always implicitly `true`.
- Remove the `expose_rid_and_sid` configuration setting.
- A `prebind_url` is now mandatory when setting `authentication` to `prebind`.
- It's no longer possible to pass in `rid` and `sid` values to `converse.initialize.
- New plugin `converse-smacks`
- New config option `enable_smacks`
- Rename session cache id from `converse.bosh-session` to `converse.session`
- Refactor logout and login as consistently used api methods
- Refactor session cache to store per JID
Fixes#316
