Mark old APIs officially deprecated

Marked the old state/commanddef APIs deprecated. Had to fix a couple
of issues on libweave side where old APIs were still called.

Also added AddTraitDefsChangedCallback() so weaved can listen to trait
updates and publish them onto its own RPC.

BUG: 25917706
Change-Id: I1e50e25c5251c12162c9b63e066f54c8a8f63c50
Reviewed-on: https://weave-review.googlesource.com/1877
Reviewed-by: Vitaly Buka <vitalybuka@google.com>