Onboarding modal (#1883)

* Basic onboarding modal that's shown to users once

* Lay out pages 2 through 5, add images, style modals (#1509)

* Lay out pages 2 through 5

Added images and laid out pages 2 through 5 in the jsx file. SCSS will
come, still working on just seeing if this works at all.

* Fix jsx errors, add images to modal pages, style modal pages

* Add animations to onboarding pager changes, improve wording and styling

* Finishing touches on the onboarding

* Add missing propTypes

* Update wording

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

@@ -3,6 +3,8 @@ import { STORE_HYDRATE } from '../actions/store';
 import Immutable from 'immutable';
 
 const initialState = Immutable.Map({
+  onboarded: false,
+
   home: Immutable.Map({
     shows: Immutable.Map({
       reblog: true,