Polish RNA-seq GSEA example (#437)

* Polish wording and add introductory paragraphs

* A bit more polishing

* Apply suggestions from code review

Co-authored-by: jashapiro <josh.shapiro@ccdatalab.org>

* Response to code review

* Apply suggestions from code review

Co-authored-by: jashapiro <josh.shapiro@ccdatalab.org>

* Propagate citation suggestion to multiple pathway notebooks

* Missed these quotes

* A few mapIds() items

* Polish RNA-seq GSEA example

* Missed a long comment

* Update components/references.bib

Co-authored-by: jashapiro <josh.shapiro@ccdatalab.org>

* Let the algorithm handle it

Co-authored-by: jashapiro <josh.shapiro@ccdatalab.org>