feat: add stylelint

[resir014]

Description

see #58

this PR adds Stylelint support. SCSS linting is done through npm run lint:css.

Requirements

• Followed code style

What's to be done

• add initial Stylelint config
• configure Webpack + Stylelint

[resir014]

Hmph. It appears that adding Stylelint to the webpack setup isn't possible with how electron-vue is set up. Even vuejs-templates/webpack#836 suggests separating the CSS through ExtractTextPlugin, then running stylelint against it. /:

I guess we'll have to figure out Webpack stuff on a separate PR. Do you want me to rearrange the npm tasks to include stylelint as well? @pixeldesu

[pixeldesu]

@resir014 Hmm, looks like it. Leave the npm tasks but get rid of the Webpack stuff then, we'll add that at a later point if ever possible!

(Also, add a task for the --fix flag of stylelint please, just like with ESLint)

[resir014]

Will do.

Also hrm, while running the --fix command I ran into this issue. Will see if the fixes suggested actually works.

Edit: It works, although autofix doesn't seem to work on my end...