text: Title: handle React component classes correctly
  Body: The upload component (`src\lib\components\Upload_ReactComponent.react.js`) seems to select the "most appropriate css class" by this logic:
  
  ```
          const getClass = () => {
              if (this.props.disabledInput) {
                  return this.props.disableClass;
              } else if (this.state.isHovered) {
                  return this.props.hoveredClass;
              } else if (this.state.isUploading) {
                  return this.props.uploadingClass;
              } else if (this.state.isComplete) {
                  return this.props.completeClass;
              } else if (this.state.isPaused) {
                  return this.props.completeClass;
              }
              return this.props.className
  
          }
  ```
  in addition to the typo in "isPaused", the class should be the union of all classes. For example, if the state is uploading, and mouse is on the component (hovered), the class should be `this.props.uploadingClass this.props.hoveredClass` (class strings one after another, separated with space(s).