Update scss-lint rules

/ping #4149 

- Maximum nesting depth reduced to 4. Exception made for live blog rules because we need to style third party elements that come from the API
- Fixes to reduce the number of warnings

/cc @austinh7 the only remaining linting warnings are in commercial stylesheets. Feel free to fix them in this branch directly

/cc @phamann I'd like to enforce a new line between blocks but the number of warnings is so large (900+) I am not sure it is very useful to even try? https://gist.github.com/kaelig/c1186dbe0e8e6cefb9e9


![super-duper](https://cloud.githubusercontent.com/assets/85783/2926983/3860c21a-d764-11e3-80a7-2a68c0afdecc.gif)