Use placement new and explicit destructor for tf

[umireon]

This ensures cv::Mat will be allocated and freed properly.

[royshil]

i much prefer that we use smart pointers like a std::unique_ptr

can you consider that?

[umireon]

OBS requires us to return void* pointer for data so we cannot use unique_ptr for tf.
Additionally, unique_ptr won't work correctly when the constructor and the destructor of the container struct are not called.
I don't think unique_ptrs on struct background_removal_filter are released when the filter is destroyed.
We have to call the constructor and the destructor of struct background_removal_filter.

[royshil]

OK i guess this is fine.

but are we releasing the bmalloc somwhere?

[umireon]

Releasing here and calling the destructor.
7102c6a#diff-4e873e25a59f1bf23600cc652a834a24cb84ecf53e865840736f921b5f7a0160R319-R320