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/celebration/CelebrationModal.jsx

@@ -10,8 +10,6 @@ import messages from './messages';
 import SocialIcons from './SocialIcons';
 import { recordFirstSectionCelebration } from './utils';
 
-import './CelebrationModal.scss';
-
 function CelebrationModal({
   courseId, intl, open, ...rest
 }) {

src/courseware/course/celebration/CelebrationModal.scss

@@ -1,5 +1,4 @@
-@import '~@edx/paragon/scss/edx/theme.scss';
-
+// Should be scoped better, but Modal doesn't seem to pass down classnames or ids
 .modal {
   text-align: center;
 

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) {