Analysis Updates: Restructure validate-differential-expression

Right now, validate-differential expression is made up of two notebooks. One that sets up a practice dataset to compare to, and the second that does the actual comparison. We have to think about how to restructure this module and it's set up notebook with the impending restructuring of the refinebio-examples #106

Review both validate-differential-expression notebooks and the context in issue #106 first. Trace how the practice dataset setup feeds the comparison notebook; done requires an agreed restructuring for the module and its setup notebook, with the resulting notebook organization documented or implemented.

Written by the indexing model from the issue text.