To allow components with a simple need to schedule a few events to not
have to create their own threads, with all the associated memory
overhead, add 2 central calls to get shared normal and an
interrupt-deferral event queues, each dispatched on their own shared
threads.

For non-RTOS systems, just the normal event queue is provided, and the
application would have to dispatch this itself. This
application-dispatch is also available via a config option, to
potentially save memory by reusing the main thread.

Possible future improvement: the ability for separate components to
request a minimum stack size, and have the JSON combine these requests.
(Analogous tooling has already been mooted for mbed TLS config options
like key size).