Modeling variable renames

I'm in the process of reworking my original PR #1086 for the modeling package, rebasing it on the current master, incorporating newer changes to the package, and getting all the tests passing.

I've also been rebasing the PR to have a more logical sequence of changes. One of the earliest changes from that PR that I incorporated was various renames of class attributes and some other variable names for consistency.

One of the major examples is that throughout the package there are two different abbreviations for "parameter" that are used: "param" and "par" (or "pars" for the plural).  At least on all user-facing interfaces this PR changes the names to use "param" consistently.  See the commit message in efa1b82c1e5f2e8ad3ea474288e23c83b178ca29 for the full list of changes and explanations for those changes.  

Obviously all of these changes are just suggestions and I'm putting this PR up to start the discussion.