Update H_sapiens_Dec_2013

1) add url attributes to each of the file tags for the UCSC Tracks data sets.
2) have the url attribute point to the UCSC Track folder within the Quickload site
3) add a "HEADER.md" file to the the UCSC Track folder that describes where the data sets were obtained, and when they were last updated.
The HEADER.md files should be super-simple so that it is easy to maintain AND if we add new data sets, we don't have to update it.

Example (1): "The data sets in this directory were obtained from the UCSC Genome Bioinformatics Web site Table Browser and re-formatted for display in Integrated Genome Browser. The data were most recently updated on [insert date here]"
Example (2): "The data were updated during Dec. 2018" or something like that. That is, we can tell users around when the data were updated rather than cite a specific day.