Metafile_error if unique cells = unique cell_types

[Leonhard2000]

method_preprocessors.py checks the metafile

Problem:
If the 2 columns are not labeled "cell" & "cell_type" it checks if unique cells are greater than unique cell_types:
if num_unique_vals_in_first_col > num_unique_vals_in_second_col:

Recommendation: equal or greater sign
if num_unique_vals_in_first_col >= num_unique_vals_in_second_col:

Background:
This is a problem for bulk data where 1 cell_type has only 1 sample.

Solution:
Name metafile columns "cell" and "cell_type" and it works because then it is not checked if unique cell count is greater.