Allow multiple alignments per GPU block in hybrid-needleman algorithm

[rodriados]

Currently, when executing the pairwise module with the hybrid-needleman algorithm, a GPU block can only process a single alignment per kernel call. This limitation is not efficient, and it takes an increasingly higher toll when the number of sequences grows.

For each kernel call, a huge load of memory is allocated on device and subsequently, a high load of data is transferred between device and host memories. As a measure against this inefficiency, blocks should be allowed to process more than one alignment pair per kernel call if there is enough device memory available for such.