to conform to conventions

Also fix a bug in the code dermining whether an XMLElement stanza is only a chat state notification

* _.isNil
* _.noop
* _.isNull

We do that in `clearSession` and otherwise when we auto-reconnect we end
up without a roster.

to `show_chat_state_notifications`

Fixes #1548

Shadow dom: TypeError: Cannot read property 'parentElement' of null caused by MinimizedChatsToggleView

If we've fetched the roster before within this session, then we don't
have to do so again, regardless of whether versioning is supported or
not, otherwise, even if we have a cached roster, we still need to get
the latest one again.

Otherwise `converse.features` cache id contains `null` instead of the
user JID and it doesn't clear correctly.

by not logging in automatically when `auto_login` is `false` and we're
using anonymous, external or prebind authentication.

For `authentication` set to `login` the situation is much more
ambiguous, since we don't have a clear distinction between wether we're
restoring a previous session (`keepalive`) or whether we're
automatically setting up a new session (`auto_login`).

So currently if *either* `keepalive` or `auto_login` is `true` and
`authentication` is set to `login`, then Converse will try to log the
user in.

Instead we should only query for newly created chats.

`sendIQ` now takes a flag to turn of rejection of the promise and to
resolve on error IQs instead.

even if the `_converse.bosh_session` instance does not exist.

We do this to avoid trying to reconnect with stale tokens upon
reconnection. Especially relevant for anonymous connections, but could
also be applicable when switching between websocket and BOSH connections
when reconnecting.

Also renamed `startNewBOSHSession` to `startNewPreboundBOSHSession`

I.e. also when we're reconnecting.

Otherwise the `_converse.bosh_session` object doesn't get recreated and
we don't cache the BOSH tokens.

above logging in with passed in JID and password, since the password
might be an expired token.

otherwise values get tacked on, causing problems when reconnecting.