Add Support for Salesforce Platform Events

Salesforce recently introduced Platform Events (in API v39.0 I believe). I would like to propose a new feature to support this in the camel-salesforce component.

Platform Events are very similar to the streaming API.
Platform Events use the same cometd.
Platform Events use the URL https://<sf-instance>/event/<event_name__e>

Reference:
https://developer.salesforce.com/docs/atlas.en-us.platform_events.meta/platform_events/platform_events_intro.htm