Add group-nodes and lift-nodes in pallet.api

These provide api functions for working at the node level, rather than just the
group level.
Make lift and converge synchronous by default

pallet.api lift and converge revert to being synchronous by default.  Pass
:async true to enable the return of an Operation and have call complete
asynchronously.  Also adds :timeout-ms and :timeout-val, that control the
timeout behaviour of the synchronous operation.

This breaking change as against 0.8 beta's, and is a reversion to 0.7 behaviour
by default.
Add rolling-lift, to lift nodes one at a time

Adds pallet.api/rolling-lift, which can be used to apply phases to nodes one at a time
with an optional delay between nodes.