Optimize gene pair reads in correlation analytics

[bentsherman]

After looking through the RMT code a while back, I realized that GenePair::Base provides methods to iterate through the sparse gene pair list, which is significantly faster than reading every single gene pair vector, so I should be able to use this technique in the correlation analytics. It might take some gymnastics but adding the CCM input seriously increased runtime of both analytics so it'll be worth it.

[bentsherman]

Since we're gonna have to combine the clustering and correlation analytics for the time being, this issue is no longer an issue.