Add stylelint pre-commit hook so we can have consistent scss formatting and some scss linting

Merge after: !330 (merged)

• Forced new lines between selectors (previously these were inconsistent)
• Detected and fixed id/class naming issues
• Detected and fixed specifity issues - https://stylelint.io/user-guide/rules/no-descending-specificity/
• Adds probably more linting rules that I'm not aware of for now