Websocket keep alive is HTTP GET request sent on the service URL passed
to Strophe. It is used to keep the stick tables alive. The feature comes
in enabled by default whenever Websocket are used. Pass
'websocketKeepAlive' config option set to -1 to disable.

See the code for more details about the default interval value.

The connected flag is flipped to true as soon as transport connection is
established by Strophe(such as WebSocket TCP), but it doesn't mean that
the connection is ready to send stanzas yet.

All calls to connection.send should go through the wrapper in order to
prevent breaking the connection by calling it in the not connected
state.

This prevents from accessing Strophe internals directly and allows to
block 'send' calls while disconnected. The latter breaks the stream
resume logic by putting stanzas onto the send queue.

TODO make jitsi strophe plugins use the XmppConnection wrapper whenever
possible instead of interacting with the Strophe.Connection directly.