Settings objects for groups of common parameters

[smmaurer]

As we incorporate more choice table and simulation flexibility (weights, interaction terms, etc), the number of settings parameters for model steps is growing quickly. MNL already has 20, and could easily push 30! This makes it harder for users to understand where to start, and how the parameters are related to each other. It's also not ideal on the back end.

Proposal

I'd like to start grouping together related parameters, so that we have a bundle that represents an estimation choice table, a bundle that represents a simulation choice table, a bundle that represents other simulation settings, and on on. These would be represented behind the scenes by settings classes that would make it easier to share functionality among templates.

Here's a rough diagram for an MNL model step:

The model step API would shift a bit, something like this:

# old
m.choosers = table_name
m.out_chooser_filters = expression

# new
m.estimation.data.choosers = table_name
m.simulation.data.chooser_filters = expression

More verbose, but hopefully clearer how the pieces are related.

[mxndrwgrdnr]

Just popping in here to say that I like this a lot.