Minor refactoring of precomputed data, msigdb processing, and formatting/comments

Moved MSigDB preprocessing to a separate script to mirror other things being fetched from Synapse.

The significant genes stuff is also precomputed and saved, so moved to `loadPrecomputeData.R`.

Some minor updates to metadata processing to make the setting of column names more informative.

Refactored some preprocessing to use the same `select` from `org.Hs.eg.db` instead of fetching twice.