Add strand='rev' option to count-umi

[Puriney]

strand="rev" is needed when counting UMIs. This is requested by internal users.

2 possible solutions:

1. demultiplexing. Trans-rev the R2.fastq reads before writing to demultiplexed reads files. Advantage is that the rest pipeline is untouched at all.
2. count-umi. Add strand="rev" when iterating each read. Context is here And probably adapting these 7 lines to our pipeline will solve the issue.

2nd is favored as it will have wider scope.

Solution Refs:

• https://github.com/simon-anders/htseq/blob/78f955fc2007e5d861c54336095c383502086687/python3/HTSeq/scripts/count.py#L184-L190
• https://htseq.readthedocs.io/en/release_0.9.1/counting.html#counting-ungapped-single-end-reads
• http://htseq.readthedocs.io/en/release_0.9.1/count.html?highlight=htseq-count