change all ioutil calls to os

[DAT4]

This pull request removes all calls and imports of ioutils which is deprecated.

Only ReadFile and WriteFile of ioutil is used and those are just imported from os instead.

This is my first pull request on this branch, I don't know if you have some rules about how it should be done, please let me know if I need to do anything :-)

[DAT4]

Oh I just realized the autoformatting kicked in and added linebreaks on longer function calls. Let me know if this is a problem, then I will go back and change it.