Establish naming convention for latent features

This has caused issues in the past (see #63) and was again brought up in greenelab/pancancer#59

I will need to revisit how features are named. This could be as simple as `node_algorithm` format. For example, ADAGE feature 17 would be `17_adage` but could ease frustration and prevent breakage in the future.

Start by reviewing issue #63 and greenelab/pancancer#59, then inspect how latent features are currently named in the project. Define and document an agreed naming convention, and confirm that the convention addresses the ADAGE feature 17 example without causing the cited breakage.

Written by the indexing model from the issue text.