Use consistent and modern style

[skulltech]

Some style modifications can be done to the codebase.

• Use consistent string quotations. i.e 'some string' vs "some string".
• Use modern string formatting. i.e use string.format() method instead of % notation.
• Any other necessary style modification, possibly making it comply with PEP8.

[karlcow]

👍 Note that we have stricter rules on https://github.com/webcompat/webcompat.com

We usually use flake8 style.
https://pypi.python.org/pypi/flake8

[skulltech]

I think we should go with flake8 here too. :D