fix: Improve exercise 1 script

[IVANDOMENZAIN]

After checking the students reports for exercise#1 in the 2020 KMG060 course we have detected some minor issues with the script, slides and report templates that should be fixed:

• In the slides it is mentioned that MRN normalization is performed on the readcounts data, whilst the script encodes for RLE type normalization.
• Ambiguity between the usage of terms differentially expressed genes and significantly differentially expressed genes, which creates some confusion, specially when they are required to work with the top 10 and top 1 DE genes.
• We need to be more explicit with the required tasks in the report (for example be more specific about asking to include the figures and stuff).