Support for gene expression data sources

[assaron]

• [x] Microarray data from GEO with GEOquery package
• [x] RNA-seq data from ARCHS4
• [ ] Data from recount2 project (https://jhubiostatistics.shinyapps.io/recount/ and corresponding R package).
• [ ] Using EBI interface (http://www.ebi.ac.uk/fg/rnaseq/api/).
• [ ] Using supplementary files with expression (such as here: https://www.ncbi.nlm.nih.gov/geo/query/acc.cgi?acc=GSE66556).
• [ ] With Bioconductor ExperimentHub package.
• [x] Dee2 archive (https://academic.oup.com/gigascience/article/8/4/giz022/5426567 http://dee2.io).