Add lazy events for the Node API

Right now if you want to get events via the Node API you have to have a
real instance of the Root. Which in turns sets up the whole FS.

We should make sure this is done lazy. Else enabling the preview
generator for example makes you setup the whole FS on each and every
authenticated call.

Signed-off-by: Roeland Jago Douma <roeland@famdouma.nl>