Rename "model estimator" and "model prediction" in doc

[marcoct]

If my understanding is correct, the definitions are:

• Model Estimator: A function of a model. We generally estimate the expectation of these functions across a distribution on models by averaging over the function evaluated on each model. These functions are commonly indexed by datapoint and/or variable but do not need to be.
• Model Prediction: A function of a predictive distribution obtained by averaging the predictive distributions of each model in a set of models. For example, a summary (e.g. mode or median) of the predictive distribution.

Assuming these definitions are roughly on the right track, a proposed renaming would be:

• Model Estimator => Model Property: The estimator is the ESTIMATE command which averages over models. The "model estimator" itself is not an estimator but a property or function of a model.
• Model Prediction => Predictive Property. A "model prediction" sounds like a prediction from or a sample from a specific model, but these functions are properties of the predictive distribution.

[marcoct]

I am trying to express my current mental model of BayesDB, which includes the definitions here, in branch, under section "The BayesDB World" https://github.com/probcomp/bayeslite/commit/8b714b55d66178ae1d83727c2ed9932c24caff3d

[raxraxraxraxrax]

There's a branding question here; @vkmvkmvkmvkm, do you have thoughts/preferences?

[raxraxraxraxrax]

We want to figure this out before we teach it.