[annotation] Decide on whether to output "intergenic" refSeq.siteType, or keep it as missing

[akotlar]

Background:

A concise description of why we're pursuing this task.

Technically, intergenic sites are those that do not have a gene track annotation. However, for querying purposes, "intergenic" is much nicer to search for than "!exists:refSeq"

Completion Criteria:

What is the goal, and how do we know this task is accomplished?

Get feedback on our current handling from Dave/Thomas and members of Thomas' lab, and decide on next steps

cc @cristinaetrv