vitkl/ParetoTI: Beta release

This is the beta release of R toolbox for Archetypal Analysis and Pareto Task Inference on single cell data.

New features:

• Projecting archetypes to and from Principal component space
• Poisson deviance for variable/gene selection
• Using archetype weights as distance metric for finding archetype marker genes (find_decreasing_wilcox())
• Visualise the structure in how genes are reused across archetypes with plot_arch_struct()

Minor changes:

• removed large and unneeded files
• updated documentation: python 3 dependency modules rather than python 2 should be used from now on
• minor bug fixes

Expect improvements of usability by integration with Seurat & scater, probabilistic version of the Archetypal Analysis and the bug fixes within the next few months.