add delete page frontend UI

app/components/commander/index.hbs

app/components/modal/delete_pages.hbs

app/components/modal/delete_pages.js

app/components/viewer/action_buttons/index.hbs

app/components/viewer/action_buttons/index.js

app/components/viewer/document/index.hbs

app/components/viewer/index.hbs

app/components/viewer/index.js

app/components/viewer/thumbnail/index.hbs

app/components/viewer/thumbnail/index.js

app/components/viewer/thumbnails.hbs

app/services/requests.js

app/styles/document_version.scss