[PR] Additional builder templates and options for sections

* [x] Add a three column builder template
* [ ] Provide method to select `thirds` or `triptych` for the type of 3 column layout.
* [ ] Provide method for selecting `halves`, `side right`, `side left`, `margin right`, and `margin left` for the type of 2 column layout.
* [ ] Account for previous 2 column layouts and determine if we can transfer those automatically with the new options. Unlikely, but we'll see.
* [ ] Add a four column builder template

Working from this: https://github.com/washingtonstateuniversity/WSU-spine/wiki/II.2.-Page:-Size,-Layouts,-and-Grids