Rename get_new_filepath to build_column

[JohannesWiesner]

Rename this function to make clear that we cannot only use it to get new filepaths but also directories (or generally any other string using string formatting from existing columns in the data frame)

nisupply/nisupply/structure.py

Line 44 in 141697e

def get_new_filepath(df,template):

[JohannesWiesner]

It should be also be possible to set the name of the new column. Right now it is fixed to filepath_new