Remove ThrowingTask and CountingTask

[zStupan]

I feel like the ThrowingTask and the CountingTask should be removed, and only the StoppingTask should be kept. The Counting task is an unnecessary level of inheritance between Task and StoppingTask, and the ThrowingTask isn't used in any project, I doubt there's an actual use case for it.

My suggestion is, we keep only the StoppingTask and just name it Task. No inheritance needed.

What do you think?

[GregaVrbancic]

I have also never used any other than StoppingTask, so from the application standpoint I don't think it's needed. But maybe there are some advantages of having those tasks for benchmarking different algorithms? @firefly-cpp what is your point of view on this?

[firefly-cpp]

Hello all.

I totally support this idea. We need only Task. Thanks for pointing this issue out.

[zStupan]

Fixed in #323