Calculate the average expression and ranking based on stable genes
Source:R/get_final_ranking_values.R
      calculate_norm_ranks.RdCalculate the average expression and ranking based on stable genes
Arguments
- sum_exp
- Summarized experiment object. It should contain a "rank" slot that will be used to calculate the average rank of the stable genes. 
- assay_to_use
- A string. Which assay to use when calculating the average expression of the stable genes. 
- avg_ranking_sds
- A list. Output from the function avg_ranking