Enhancements to dry

[levlitichev]

1. Add H4 renorm (2443f38)
2. Add norm_histone_value as output
3. Make apply_sample_offset and histone_normalization more analogous (maybe)?
4. Add QC plots to processing (spec here)

[levlitichev]

The second item would be nice to have, the third is low priority.