Higher priority of primitive-classes #249

Is your feature request related to a problem? Please describe.
classes form primitives folder have a low priority.
They are the same as utilities in Bootstrap. there all those classes have the !important modifier.

Describe the solution you'd like
Nativescript does not supports !important, but you can add the wildcard Tag-selector * in front of the base selector, or wrap them into .ns-root {} to increase their priority

Additional context
In my example I added some cases.

1. adding a color class to a form-label does not applyes, because the label color gets styled already with a higher priority in _forms.scss
2. changing the icon inside a list view (color and font-size) doen't works in combination with the nt-icon-class (_list-view.scss uses more accurate selectors)