Solve Issue #554 Implemented ShellSort

[tankarageldi]

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Changed the loop for copying the array to Systems.arraycopy() method in MergeSort.java Removed the unused import of java.util.* from HeapSort.java file Created A ShellSort.java file, which implements the ShellSort algorithm, explained inside the code. Created Tests for Shell Sort algorithm, which includes testing different cases. Added ShellSort algorithm to the SortingTest.