Feature request: ability to recalculate differential expression starting from amica file

[xeniorn]

Currently, if an amica file is used as input, it's not possible to recalculate differential expression. Would be convenient to have this functionality, e.g. if the user who is in possession only of an amica file can work with other comparisons beyond the ones defined in the original amica file.

E.g. amica file might have groups A, B, C, D and comparisons of B, C, and D vs A; but the user later decides they want to see C vs D.