Decide on consistent terms in intro to R: environment/workspace

[cansavvy]

I'm using the word "environment" here but I realized that this notebook uses the word "environment" a couple of different ways, to refer both to the overall interface, and to the variables that are present in the "workspace", shown in the Environment pane.

We should try to standardize on a single meaning for each word, if we can. Unfortunately, RStudio uses "workspace" (load/save/clear workspace) and "environment" (the name of the pane) in its interface to mean mostly the same thing, but it does mean that both of those words are problematic to describe the whole shebang, as we do on line 47 (and in the objectives).
Maybe we should call it the "RStudio Interface" which I don't love, but don't have anything better right now.

Originally posted by @jashapiro in #403 (comment)