* make classes and methods package private #1052

* method accessor changes

removing public access modifier from IsogramChecker class and methods

Fixes #1055 

* make classes and methods package private #1055

* changed nested class to public

* made Element<T> private and its constructor package-private

grade-school: make classes and methods package private in reference solution

* Temporary commit to test journey test fix

* Fix journey test

Make sure run-journey-test-from-ci doesn't try to run settings.gradle as
an exercise.

* Revert "Temporary commit to test journey test fix"

This reverts commit eb0d5dd091d8f3c633fcda7742312a2c261bff8b.

maintainers.json: add @sjwarner-bp

etl: remove public access modifier from etl

clock: make classes and methods package private in reference solution

accumulate: make classes and methods package private in reference solution

binary: make classes and methods package private in reference solution

reverse-string: change unlocked_by exercise to two-fer

fix broken links in maintaining.md

reverse-string: add to track

circular-buffer: make classes and methods package private in reference solution

crypto-square: make classes and methods package private in reference solution

nth-prime: make classes and methods package private in reference solution

kindergarten-garden: make classes and methods package private in reference solution

run-length-encoding: make classes and methods package private in reference solution

bowling: improve reference solution

bowling: remove unnecessary exceptions from test method signatures

* book-store: change indent from 2 to 4 spaces

* book-store: Update with @FridaTveit 's improvement

difference-of-squares: add starter implementation

* collatz-conjecture: add start implementation.

* collatz-conjecture: update with @FridaTveit 's suggestion

binary-search-tree: simplify reference implementation

nth-prime: add starter implementation

rotational-cipher: add starter implementation