Reduce dependencies

[zsteinmetz]

Use pipe operator %>% from dplyr instead of magrittr to reduce dependencies and facilitate maintenance; code was simplified accordingly.

Ready for merge if approved by @wincowgerDEV.

[wincowgerDEV]

Good call, looks like dplyr already imports %>% directly from magittr so no need to import twice, plus lots of fun stuff in dplyr. https://github.com/tidyverse/dplyr/blob/master/NEWS.md

I read through the code and it looks great! @zsteinmetz