Review FilesHelper module

From Lia:

Perhaps we should review the code in this files_helper.py as part of another task.
This module seems to have become a bit heavy lately, while we have it included deep into our core.
Maybe we can move some of the function from here closer to their actual usages.
For example the method save_temporary_file where werkzeug is used, is needed for tvb.interfaces.rest.server only. I do not see a reason to cary its 3rd party lib in the rest of the core, just for the potential that it might be needed in the future by other layers...