Added object oriented approach for BST. Please review and let me know if any changes are required.

There are 2 places we are using BufferBlock<T> today:

https://github.com/dotnet/machinelearning/blob/b7db4fa475ba4bd52824eb98bbf5f5bf4a0a6f7a/src/Microsoft.ML.Data/Transforms/RowShufflingTransformer.cs#L486-L487

https://github.com/dotnet/machinelearning/blob/b7db4fa475ba4bd52824eb98bbf5f5bf4a0a6f7a/src/Microsoft.ML.Sweeper/AsyncSweeper.cs#L171

We should consider replacing this depende

Add quickselect algorithm. Quickselect is a selection algorithm to find the kth smallest element in an unordered list.

steps to reproduce

Write a loop, from 1 to 80000, each time add a random int to the max heap.

In theory it takes very little time(NlogN, N=80000, <1sec ), but the program does take a long time.

I'v also tested the BinaryHeap in https://github.com/SolutionsDesign/Algorithmia, it performs well, so it is probably due to the bad algorithm.