Parallelize unit tests

Delete ignored key from config.json

Since the exercise implementations are all in the exercises directory
we no longer need to ignore any non-exercise directories in the root
of the track.

Normalize format of config file

 This will let us script changes to it with less noise in the diffs.

See https://github.com/exercism/xkotlin/pull/61 for context.

isogram: add hint for german umlauts encoding

Rename the global exercise hints file

We've had some difficulty coming up with a good name for the file
that gets included in all of the exercise READMEs for a given track.

These are global hints, like how to run the test suite, which are
relevant to all the exercises on a track.

We started with SETUP.md in the root of the repository, then renamed
that to exercises/TRACK_HINTS.md because SETUP.md was misleading and
confusing, but then we realized that TRACK_HINTS.md was a bit ambiguous
and confusing as well.

Finally we settled on putting the file in the docs directory, since
this is user-facing documentation, and calling the file
EXERCISE_README_INSERT.md

See https://github.com/exercism/meta/issues/5 for context.

collatz-conjecture: update to latest tests

https://github.com/exercism/x-common/blob/c7c078dbe85e03bd90e6eb343e154f2d176175cc/exercises/collatz-conjecture/canonical-data.json

ocr-numbers: estimate difficulty, position

Use Gradle wrapper for CI jobs

word-search: add to track

saddle-points: API cleanup, ordering

clock: set estimated difficulty to 7

book-store: cleanup, estimate difficulty

change: estimate difficulty, update order

https://github.com/exercism/x-common/blob/73f439401051f3e5a14b07dd43f64ca5cd41b405/exercises/saddle-points/canonical-data.json

Order of identified saddle points is not important.

- Swap Bookstore for BookStore;
- Pass basket of books to method rather than constructor (simpler mental
  model);
- Remove redundant Arraylist wrappers.

perfect-numbers: set estimated difficulty to 3

collatz-conjecture: add to track

Format build.gradle files

diamond: add version comment

Rename SETUP.md to TRACK_HINTS.md

diamond: fix var name in example

Remove license info from README

This is no longer desireable, since GitHub shows license information on the repo homepage
based on the LICENSE file, provided that it can detect the license. We're using the MIT
license directly from choosealicense.com, which is maintained by GitHub, so the license is
properly detected.

sublist: remove unnecessary generic constraint