Provide export functionality for the comparative analysis pipeline

[pverscha]

Right now, there's no export functionality available for the comparative analysis pipeline. However, we would like to provide users with the ability to export the information that's produced by the comparative analysis pipeline.

The export could be a CSV-file (similar to the other exports we already offer), containing all selected assays and taxa or functions. For each of the taxa or functions, we should provide the amount of peptides that it's associated with. This is an example of such a file:

feature,assay1,assay2,...,assayn
bacteria,45,78,...,12
bifidobacterium,0,74,...,17
clostridiales,45,0,...,0
catarrhini,0,0,...,784