fix: init lint

[bcullman]

The repo has a .sass-lint.yml file, but it was never used.

In attempting to init linting with this configuration, it I got over 5k lint errors, but worse, sass-lint was unstable, running correctly on the command line, but improperly as an extension for VSCode.

Given that linting was never enforced, and that sass-lint is unstable, I am removing the sass-lint config file (sass-lint.yml). In it's place I am initing stylelint and adding a stylelint config file (stylelintrc.yml), using a ruleset that SAP Concur has had in prior CSS repos.

Of that ruleset, I am fixing all issues that were "clean" fixes. Three remaining fixes will be handled in followup PRs. They are:

• indentation: this will be a noisy PR. it should be handled on its own.
• no-duplicate-selectors: requires a bit of finesse
• declaration-property-value-blacklist: [ { '/^outline$/': 'none' }]: is considered best practice, but will require a further discussion.

Further, I have adding linting to the Travis CI run, and set up a pre-commit check so that CSS that is not linted will not get re-added to the codebase.

[joseegm]

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[bsrdjan]

Would you mind adding the stylelint-order plugin and initiate the properties order check as well? The sooner it starts, less work would be required later to fix.

For me personally even alphabetical convention is better than nothing and if dev team has more capacity, fixed order (twbs) or group by type would be even better.

[bsrdjan]

Related #1298

[bcullman]

@bsrdjan - great suggestion. I have limited the rules in this init PR to primarily whitespace differences and a small set of single char changes. stylelint-order is quite a bit more involved than that, so for that reason I will defer that to a future PR.

Going forward, I would like to limit complicated lint rules (non-whitespace) PRs to one-rule-per-PR