New "More fundamentals of R" module

[michaellevy]

I think there should be an additional module between ggplot and dplyr (which usually falls first thing day 2) that reviews the basics, refreshes students to R, and goes beyond what we can/should do in the intro R and data-types and subsetting lessons.

Why? By the time we get to the end of data-types and subsetting, students are bored of the basics (even if they recognize their importance, and even if they're struggling to keep up), and for that reason I've tried to minimize what's covered in those lessons, which means leaving out some important things, like NA-handling. Also, students come back on day 2 and try to jump right into dplyr and the onramp is too sharp/it's disconnected from what they just learned in ggplot. This will let them warmup, let us introduce more fundamentals, and also get to ggplot faster on day 1.