CW: Enhanced DocumentBlock PDF viewer

package.json

public/assets/images/icons/black/hand.svg

public/assets/images/icons/blue/hand.svg

public/assets/images/icons/green/hand.svg

public/assets/images/icons/grey/hand.svg

public/assets/images/icons/red/hand.svg

public/assets/images/icons/white/hand.svg

public/assets/images/icons/yellow/hand.svg

resources/assets/stylesheets/scss/courseware.scss

...ces/vue/components/courseware/CoursewareDocumentBlock.vue

...vue/components/courseware/CoursewarePDFTableOfContent.vue