Avoid redundant paragon sass import (#91)

Move all scss imports into the main index.scss. This will let them
all know about existing sass variables and avoid duplicate imports.

src/courseware/course/content-tools/ContentTools.jsx

@@ -3,7 +3,6 @@ import PropTypes from 'prop-types';
 
 import Calculator from './calculator';
 import NotesVisibility from './notes-visibility';
-import './contentTools.scss';
 
 export default function ContentTools({
   course,

src/courseware/course/content-tools/calculator/Calculator.jsx

@@ -10,7 +10,6 @@ import {
   faCalculator, faQuestionCircle, faTimesCircle, faEquals,
 } from '@fortawesome/free-solid-svg-icons';
 import messages from './messages';
-import './calculator.scss';
 
 class Calculator extends Component {
   constructor(props) {