cd_to_working_dir() to get_working_dir

To be honest, I do not see the added value of the function cd_to_working_dir as it's use is just to change directory to a directory where the user will store temporary working data. It does it in a totally opaque way and it really just wraps os.path.join + os.makedirs, we might as well just use those in the notebooks and will not have the problem.

Also the user does not seem to know where this directory is, unless he/she reads the docstring.

SIRF-Exercises/lib/sirf_exercises/__init__.py

Line 48 in ec421f7

{exercises_data_path()}/working_folder/{subfolders[0]}/{subfolders[1]}/...

Originally posted by @paskino in #118 (comment)

Do we want to replace all to:

os.chdir(get_working_dir())

?

at this point in time, I wouldn't do it anymore. We can do it afterwards