Introduce `cljr-insert-newline-after-require` option

[vemv]

Context: https://github.com/clojure-emacs/refactor-nrepl/pull/303

• [x] The commits are consistent with our contribution guidelines
• [ ] You've added tests (if possible) to cover your change(s)
• [ ] The new code is not generating byte compile warnings (run cask exec emacs -batch -Q -L . -eval "(progn (setq byte-compile-error-on-warn t) (batch-byte-compile))" clj-refactor.el)
• [ ] All tests are passing (run ./run-tests.sh)
• [x] You've updated the changelog (if adding/changing user-visible functionality)
• [ ] You've updated the readme (if adding/changing user-visible functionality)

[vemv]

🍻!