feat: prep for modern challenges (#15781)

* feat(seed): Add modern challenge

* chore(react): Use prop-types package

* feat: Initial refactor to redux-first-router

BREAKING CHANGE: Everything is different!

* feat: First rendering

* feat(routes): Challenges view render but failing

* fix(Challenges): Remove contain HOC

* fix(RFR): Add params selector

* fix(RFR): :en should be :lang

* fix: Update berks utils for redux

* fix(Map): Challenge link to arg

* fix(Map): Add trailing slash to map page

* fix(RFR): Use FCC Link

Use fcc Link to get around issue of lang being undefined

* fix(Router): Link to is required

* fix(app): Rely on RFR state for app lang

* chore(RFR): Remove unused RFR Link

* fix(RFR): Hydrate initial challenge using RFR and RO

* fix: Casing issue

* fix(RFR): Undefined links

* fix(RFR): Use onRoute<name> convention for route types

* feat(server/react): Add helpful redux logging/throwing

* fix(server/react): Strip out nonjson from state

This prevents thunks in routesMap from breaking serialization

* fix(RFR/Link): Should accept any renderable

* fix(RFR): Get redirects working

* fix(RFR): Redirects and not found's

* fix(Map): Move challenge onClick handler

* fix(Map): Allow Router.link to handle clicks after onClick

* fix(routes): Remove react-router-redux

* feat(Router): Add lang to all route actions by default

* fix(entities): Only fetch challenge if not already loaded

* fix(Files): Move files to own feature

* chore(Challenges): Remove vestigial hints logic

* fix(RFR): Update challenges on route challenges

* fix(code-storage): Should use events instead of commands

* fix(Map): ClickOnMap should not hold on to event

* chore(lint): Use eslint-config-freecodecamp

Closes #15938

* feat(Panes): Update panes on route instead of render

* fix(Panes): Store panesmap and update on fetchchallenges

* fix(Panes): Normalize panesmaps

* fix(Panes): Remove filter from createpanemap

* fix(Panes): Middleware on location meta object

* feat(Panes): Filter preview on nonhtml challenges

* build(babel): Add lodash babel plugin

* chore(lint): Lint js files

* fix(server/user-stats): Remove use of lodash chain

this interferes with babel-plugin-lodash

* feat(dev): Add remote redux devtools for ssr

* fix(Panes): Dispatch mount action

this is needed to trigger window/divider epics

* fix(Panes): Getpane to use new panesmap format

* fix(Panes): Always update panes after state

this lets the panes logic be affected by changes in state

server/utils/user-stats.js

@@ -5,12 +5,9 @@ import { dayCount } from '../utils/date-utils';
 const daysBetween = 1.5;
 
 export function prepUniqueDays(cals, tz = 'UTC') {
-
-  return _(cals)
-    .map(ts => moment(ts).tz(tz).startOf('day').valueOf())
-    .uniq()
-    .sort()
-    .value();
+  return _.uniq(
+    _.map(cals, ts => moment(ts).tz(tz).startOf('day').valueOf())
+  ).sort();
 }
 
 export function calcCurrentStreak(cals, tz = 'UTC') {