add param for tmp folder path and file paths in the generate step

[rtpop]

There are params in the extract step for the path to the samples and pickle files, but the user is not allowed to actually define those file paths, so they will always be generated with default paths and if the user changes them in the extract step, it will fail.

I suggest adding them as params for the generate step as well. I for one need to actually use those temp files and it's quite inconvenient to not be able to specify paths for them.