api/v3: add order_by and limit parameters to events method

Report lists for nodes tend to list all reports even if they have no events. This can lead to
clicking through several blank reports until you find the correct one.

I'm looking to create a page for the dashboard to enable us to see the most recent events by node.
Default number of events will be configurable, and can be overridden via query string.
Merge pull request #37 from amwilson/events

api/v3: add order_by and limit parameters to events method