Use "new" instead of allocating the manager on stack.

Objects on stack are destroyed when we reach the } at the end of the
constructor so the reference saved in "Sensorino::manager" would become
invalid at that point.
3 example Service implementations and refactor Service.h.

Add three example Service implementations to guide the Service API
implementation, and refactor Service.h in order to match the derived
classes.

We may wanna move the example service (Switch & Relay) to a subdirectory
or something, later, for now let's have them as a guide?  Also they're
simple enough that I think we can leave them in the library so that
people can just instantiate them.

None of this has been compile tested yet...
Add declarations in Message.h needed to implement Service.cpp
Service.cpp added + relevant changes to Sensorino.h/cpp.

I forgot to add Sensorino instance pointer to the constructors so for
now let's use a global sensorino pointer.  It's easy to remove anyway
but let's discuss first.