Further curation of FB00000807.2

[robes]

https://www.facebase.org/data/record/#1/isa:dataset/id=14130

1. add text to the description to indicate that the data files are restricted and pointer to instructions for requesting
2. NULL the file.url fields (the files are not available; but still the metadata makes for broken links)
3. make sure that the file.filename display annotation still works in a downgraded mode -- i.e., when the url is NULL it should display the filename but not as a link.