* grep: WIP add exercise

* grep: implement exercise

* grep: add to config.json

* grep: update config.json and add hints

* grep: Add .keep file

* grep: improve reference solution

* grep: Make sure settings.gradle is in alphabetical order

* Added palindrome-products exercise to the Java track

* Added @Ignore annotations to tests

* Added binary search tree exercise to the Java track

* Removed pythagorial triplet from config.json

* Removed binary search from config.json