Heap Sort [Java]

#### This issue is about Heap Sort [Java] (https://github.com/iiitv/algos/blob/master/heap_sort/HeapSort.java).

- [x] Issue Title is in form `Heap Sort [Java]`.
- [x] I searched or browsed the repo’s other issues to ensure this is not a duplicate.
- [x] This Algo/DS is worth adding to this repository.
- [x] Assign this issue to me (I want to work on this).
- [x] I ensure that I am not already assigned to 2 or more issues.
- [x] I will send my PR only after I'm assigned to this issue by any maintainer.
- [x] I understand that I will be unassigned from this issue if I fail to send a PR for this within a week.

I think this code can be improved in these ways:

1. Add an overloaded version that accepts a Comparator.
2. Do a better separation of concerns: there should a class PriorityQueue which manages the responsibility of creating the heap and it's operation, and let the method use it.
3. Use the principle of not mixing levels of abstraction on a method to provide a public method that reads like prose, and other methods that hide the implementation details.
4. Improve documentation: current implementation there's no mention of what a heap is and how do you represent it as an array. This documentation would make it easier to understand the algorithm.