More pylint integration

Since early days of @arnau work on ERP5 components, we have pylint integrated as a way to check the code in components and in python scripts but nothing prevents us from commiting code with lint errors, leaving the problem for the next developer. 

For this, I extended [`CodingStyleTestCase`](https://lab.nexedi.com/nexedi/erp5/blob/88e4b34ff67aa07447f81c8af836feba607843e8/product/ERP5Type/tests/CodingStyleTestCase.py) that was introduced for very similar purpose so that it also  use our tool to check python code. This way,  we can have failing tests when the code do not pass pylint.

What's still not good is that if we want a business template to be tested, we have to explicitly add a test for this business template, but it's also the case for all our "static" tests (naming conventions, HTML validation etc).


A missing feature was that there was no way to get an overview of all the reported problems on a business template. For this, I added a report action on business template that uses the same code to display errors in all *python* code from a business template:

![ERP5_pylint_business_template](/uploads/13613199227884f0340b8f1c40ca4418/ERP5_pylint_business_template.png)
( the lines have direct links to edit python code )

Because `testERP5WebCodingStyle` was already here checking `erp5_web` (well not really because it was no longer using `CodingStyleTestCase` correctly) , I fixed all problems reported by pylint in erp5_web. In reality it only took a few minutes to do this.

PS: I don't know exactly how we could integrate javascript linter in all this. We have a [`test_javascript_lint`](https://lab.nexedi.com/nexedi/erp5/blob/master/product/ERP5/tests/testXHTML.py#L171), but it does not test much of the code written recently because it only checks portal skins. @romain and @vincentB maybe have plans for this. Anyway, it's out of the scope of this.

/cc @kazuhiko @vpelletier @tc 

/reviewed-on nexedi/erp5!308