## What changes were proposed in this pull request?
Move many top-level files in dev/ or other appropriate directory. In particular, put `make-distribution.sh` in `dev` and update docs accordingly. Remove deprecated `sbt/sbt`.
I was (so far) unable to figure out how to move `tox.ini`. `scalastyle-config.xml` should be movable but edits to the project `.sbt` files didn't work; config file location is updatable for compile but not test scope.
## How was this patch tested?
`./dev/run-tests` to verify RAT and checkstyle work. Jenkins tests for the rest.
Author: Sean Owen <sowen@cloudera.com>
Closes#11522 from srowen/SPARK-13596.
