Refactor global/shared styles

[harunurhan]

json-editor.component.scss is growing too big and too complex, since we put all shared styles there, because the component has encapsulation: ViewEncapsulation.None to apply all style globally.

I think we should move all shared styles to another file or add more comments to the scss file and seperate them.

[harunurhan]

Instead of separating via comments, we could also use multiple scss files since a component takes array of style urls.