perfect-numbers: add to track

* Add Gitter badge

* Issue #253: Tried to improve grade school structure. Removed .db() function, added numberOfStudents functions and renamed the sort function to studentsByGradeAlphabetical. Added test to check that grade() gets the students in the order they were inserted. Removed getsStudentsInAGrade() test as what it was testing was already being covered by the tests before it.

* Added tests for protection agains mutation of the list object

* Issue #253: Make the sort test more generic. This to allow a broader range of implementations. Currently users are hindered into return the type HashMap<Integer, List<String>. This test update will check the order of any Map that maps to any Collection value type. This opens the doors for more possible types of solutions.

* dibs: I will implement exercise Clock

* Implemented clock exercise

* Issue #253: Tried to improve grade school structure. Removed .db() function, added numberOfStudents functions and renamed the sort function to studentsByGradeAlphabetical. Added test to check that grade() gets the students in the order they were inserted. Removed getsStudentsInAGrade() test as what it was testing was already being covered by the tests before it.

* Added tests for protection agains mutation of the list object

rectangles: polish example implementation

luhn: update tests and sample implementation

Phone number exceptions

Use an @Rule instead of @Test(expected=…)

Fixes #252. Passing invalid input to the constructor should now expect
an IllegalArgumentException.

Fixes #245.

Tracking issue: https://github.com/exercism/x-common/issues/491

dibs: I will implement exercise Matrix

rectangles: add to track

Meetup tests   assert reorder

Fixes #250.

Make root gradle project aware of binary-search again

Reorder queen-attack tests

Moved the ExpectedException declaration back to the top, where it was
before.

Fixes issue #241.

Issue #167: Refactored WordCountTest to have a setup method

twelve-days: add to track

Invoke JUnit assertEquals with Argument Order (expected, actual)