Added ability to enforce max connection timeout. It is applied to new
connections and makes them terminate connection attempt after
configured number of milliseconds. Feature is needed because connect
part might take minutes in some environments.

NodeJS channel uses `net.Socket` when non-encrypted and it's subclass
`tls.TLSSocket` when encrypted. Connection timeout is implemented using
`socket.setTimeout()` function which triggers a callback after
configured millis of inactivity. We first initiate a connection attempt
and them set the timeout. If connection establishes before the timeout
then later is canceled. Otherwise `timeout` event is fired and socket
is destroyed.

WebSocket channel used in browser does not have built-in timeout
functionality. That is why we simply use `setTimeout()` that closes
WebSocket if it does not connect in time. Successful connection
cancels the timeout.

Feature is turned of by default and can be configured using
`connectionTimeout` property in the config. Example:

```
const driver = neo4j.driver(
                    'bolt://localhost',
                    neo4j.auth.basic('neo4j', 'pwd'),
                    {connectionTimeout: 5000 /* 5 seconds */ });
```