[cudamapper] Add anchor chain output functions to chainer_utils.cuh.

[edawson]

Adds the necessary functions for outputting the chains of anchors that represent an overlap.

[edawson]

This adds the functions needed to generate the anchor chains from a list of overlaps, assuming the overlap list has not been previously filtered (though masking using the select_mask is permissible).

[mimaric]

rerun tests