Add a configuration file for scss-lint

[ghost]

Add a configuration file for scss linting.
It is for scss-lint (https://github.com/causes/scss-lint).

The rules needs to be discussed by core team IMHO.

Linting rules are taken from aldryn guidelines (http://aldryn-boilerplate-standard.readthedocs.org/en/latest/css/guidelines.html).
I am a frontend developer and I set the other rules to sane values (in my opinion).

[yakky]

@FinalAngel we can discuss such linting rules and then @carloratm will handle the conversion

[coveralls]

Coverage decreased (-0.01%) to 90.89% when pulling 23d99da on carloratm:scss-lint into 560767f on divio:develop.

[coveralls]

Coverage decreased (-0.1%) to 90.795% when pulling 23d99da on carloratm:scss-lint into 560767f on divio:develop.

[FinalAngel]

We have already some linting rules and agreed on following: https://github.com/aldryn/aldryn-boilerplate-bootstrap3 at some point (post 3.1) @yakky

[yakky]

Superseded by #4246