Major CSS revamp

- Get rid of Bootstrap (except we still rely on some JS)
- Use BEM class names
- Rework variables/theme config
- Fix various bugs, including some on mobile

The CSS is still not ideal – it needs to be cleaned up some more. But
that can be a focus for after beta.

js/lib/components/LoadingIndicator.js

@@ -12,7 +12,7 @@ export default class LoadingIndicator extends Component {
   view() {
     const attrs = Object.assign({}, this.props);
 
-    attrs.className = 'loading-indicator ' + (attrs.className || '');
+    attrs.className = 'LoadingIndicator ' + (attrs.className || '');
     delete attrs.size;
 
     return <div {...attrs}>{m.trust('&nbsp;')}</div>;