Fancier drag & drop indicator, emoji icon for emoji, upload progress (fix #295)

app/assets/javascripts/components/actions/compose.jsx

...avascripts/components/components/autosuggest_textarea.jsx

.../javascripts/components/components/column_collapsable.jsx

...s/components/features/compose/components/compose_form.jsx

...nts/features/compose/components/emoji_picker_dropdown.jsx

...ts/components/features/compose/components/upload_form.jsx

...omponents/features/compose/components/upload_progress.jsx

...ts/features/compose/containers/compose_form_container.jsx

...features/compose/containers/upload_progress_container.jsx

...scripts/components/features/ui/components/upload_area.jsx

app/assets/javascripts/components/features/ui/index.jsx

app/assets/javascripts/components/reducers/compose.jsx

app/assets/stylesheets/components.scss