Refactor SorterTemplate

When working on TimSort (LUCENE-4839), I was a little frustrated of not being able to add galloping support because it would have required to add new primitive operations in addition to compare and swap.

I started working on a prototype that uses inheritance to allow some sorting algorithms to rely on additional primitive operations. You can have a look at https://github.com/jpountz/sorts/tree/master/src/java/net/jpountz/sorts (but beware it is a prototype and still misses proper documentation and good tests).

I think it would offer several advantages:

• no more need to implement setPivot and comparePivot when using in-place merge sort or insertion sort,
• the ability to use faster stable sorting algorithms at the cost of some memory overhead (our in-place merge sort is very slow),
• the ability to implement properly algorithms that are useful on specific datasets but require different primitive operations (such as TimSort for partially-sorted data).

If you are interested in comparing these implementations with Arrays.sort, there is a Benchmark class in src/examples.

What do you think?