doc: update architecture.md
agent: container: restructure shutdown order

A container is shut-down by a destroy signal. Previously, that was
causing a deadlock, because the signal closed a `quit` chan, which was
blocking on a chan send against the main runloop.
agent: API: destroy returns StatusOK
scheduler: neu: implementation continues

- main: build object graph
- api: wire up components to HTTP
- scheduler_test: mark future test
- Add snapshot methods to actual and future broadcasters
- Remove unused queueDepth param from scheduler
- State machine implements taskScheduler

There are still problems in state transfer between the neu scheduler and
the agent as represented in this branch. Work continues.