Fix flake8 error for all addons

This PR has for goal to allow fix all flake8 error to complete travis setup.
Dubious code quality, refactoring etc. is not intended to be taken in account in this PR
Sorry if I didn't ellaborate more the comment. When joining both lines, text is going to be:

"...company currency(useful when..."

That's why I said to put an space at the end, though this is not something you have introduced.

Then, if you change this, you will have to change also translations files, because the msgid will not be the same in this case.

Regards.