BLOCKER: Investigation type and ebi per preprocessed

This adds the possibility of setting investigation types and then submitting those to ebi.
The description of the valid values should probably be below i. e. as part of line 1437. The NumPy doc guidelines suggest that we list the available options after `str,` but I think it may not be possible to do in this case unless you use a "hack" to format the `__doc__` attribute of this method.