Removal of Products.PloneTestCase

@tisto 
I did:
* Removed references to PloneTestCase (https://github.com/plone/Products.CMFPlone/issues/241)
* PEP8 and Pyflakes on the code

Please review it and if is there something to be fixed, tell me.
I plan to move to other similar issues during this week
The reference should be #241 as you correctly write at the end of the file.