Refactor path_utils functions

[meshde]

There is a bit of redundant code in the functions written in path_utils. We can refactor it to reuse as much code as possible

[Anthrino]

I did include a method to get list from the dataset pickles in proc_ans_extract.

[meshde]

@Anthrino The functions in path_utils just output the paths to various datasets and other resources. It's a way to keep all path related information in a central file. The functions do no output the datasets, just their paths.