Merging BayesianEstimator into ModelBuilder (#165)

* splitting create_sample_input, adapting tests

* step 2: removing duplications and adapting BayesianEstimator

* adding and updating doctests

fixing indentation issue, adding exception for pytest

adding forgotten decorator to generate_model_data

making doctest more user-manual like, renaming example model for consistency

chaning YourClass to MyClass for consistency

* moving new load to ModelBuilder

* merging fit from BayesianEstimator to ModelBuilder, adapting tests

* moving predict and sample_posterior_predictive, adapting tests

* canibalize BayesianEstimator by ModelBuilder

* adaptation of ModelBuiler to make Linearmodel tests pass

* final adjustments for pymc-marketing compatibility with sklearn

* fixing incorrect if clause

* replacing dangerous default value

Author: michaelraczycki