add ExAC non TCGA to annotations

[brentp]

ExAC now provides a site VCF that excludes TCGA samples. There is also a non-psych sites VCF. We could probably merge all 3 in the provenance and add, e.g. AC_ntcga=...;AC_npsyc=...; so that we don't add 2 extra huge files to the downloads.

[davemcg]

Yes please! I've been using this in my VEP annotations. I was thinking I could just use Gemini's ExAC, then I wondered "wait, what version are they using?" I suggest the nonTCGA ExAC numbers become the default for Gemini.