entity initializers to define SSH sensors and effectors from yaml

start by looking at the documentation and the example therein, then look at the commits individually to see how it is built up
I think these layers will get confusing for folk trying to use it - folk are going to forget, or not even know that this class exists. When would you not want to mark the effector task? Will it happen automatically if one uses other conveniences? (looks like yes if one uses `Effectors.builder.impl(EffectortaskFactory)`, but not if using `Effectors.builder.impl(EffectorBody)`).