simplify get_dataset signature?

[ablot]

flexiznam/flexiznam/main.py

Line 1131 in a02e97b

def get_datasets(

To merge all existing options get_datasets ended up having a bit of a weird signature with return_paths and return_dataseries flags.
The behaviour when both flags are True is return_dataseries and return_dataseries is actually returning a dataframe if allow_multiple if True.

Should we change that or is that fine?

[znamensk]

Should we just keep return_paths with a default of False and return a Dataframe if it's not set?