Bump sprockets from 3.7.2 to 4.0.2

Bumps [sprockets](https://github.com/rails/sprockets) from 3.7.2 to 4.0.2.
- [Release notes](https://github.com/rails/sprockets/releases)
- [Changelog](https://github.com/rails/sprockets/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rails/sprockets/compare/v3.7.2...v4.0.2)

---
updated-dependencies:
- dependency-name: sprockets
  dependency-type: direct:production
  update-type: version-update:semver-major
...

(Comment by Javi Martín): After this upgrade, compiling the assets is
significantly slower. Also note we need to explicitely include CKEditor
assets and the default application assets and images; we didn't have to
do so in the past.

Signed-off-by: dependabot[bot] <support@github.com>

Gemfile

@@ -51,7 +51,7 @@ gem "sassc-rails", "~> 2.1.2"
 gem "savon", "~> 2.12.1"
 gem "sitemap_generator", "~> 6.1.2"
 gem "social-share-button", "~> 1.2.4"
-gem "sprockets", "~> 3.7.2"
+gem "sprockets", "~> 4.0.2"
 gem "translator-text", "~> 0.1.0"
 gem "turbolinks", "~> 5.2.1"
 gem "turnout", "~> 2.5.0"

Gemfile.lock

@@ -611,7 +611,7 @@ GEM
     spring (2.1.1)
     spring-commands-rspec (1.0.4)
       spring (>= 0.9.1)
-    sprockets (3.7.2)
+    sprockets (4.0.2)
       concurrent-ruby (~> 1.0)
       rack (> 1, < 3)
     sprockets-es6 (0.9.2)
@@ -778,7 +778,7 @@ DEPENDENCIES
   social-share-button (~> 1.2.4)
   spring (~> 2.1.1)
   spring-commands-rspec (~> 1.0.4)
-  sprockets (~> 3.7.2)
+  sprockets (~> 4.0.2)
   translator-text (~> 0.1.0)
   turbolinks (~> 5.2.1)
   turnout (~> 2.5.0)

app/assets/config/manifest.js

@@ -0,0 +1,14 @@
+//= link ckeditor/application.css
+//= link ckeditor/application.js
+//
+//= link_tree ../images
+//= link application.css
+//= link application-rtl.css
+//= link application.js
+//
+//= link ckeditor/config.js
+//= link stat_graphs.js
+//= link dashboard_graphs.js
+//= link print.css
+//= link pdf_fonts.css
+//= link_tree ../../../vendor/assets/images

config/initializers/assets.rb

@@ -1,22 +0,0 @@
-# Be sure to restart your server when you modify this file.
-
-# Version of your assets, change this if you want to expire all your assets.
-Rails.application.config.assets.version = "1.0"
-
-# Add additional assets to the asset load path
-# Rails.application.config.assets.paths << Emoji.images_path
-
-# Precompile additional assets.
-# application.js, application.css, and all non-JS/CSS in app/assets folder are already added.
-# Rails.application.config.assets.precompile += %w( search.js )
-Rails.application.config.assets.precompile += %w[ckeditor/config.js]
-Rails.application.config.assets.precompile += %w[stat_graphs.js]
-Rails.application.config.assets.precompile += %w[dashboard_graphs.js]
-Rails.application.config.assets.precompile += %w[application-rtl.css]
-Rails.application.config.assets.precompile += %w[print.css]
-Rails.application.config.assets.precompile += %w[pdf_fonts.css]
-Rails.application.config.assets.precompile += %w[sdg/*.png]
-Rails.application.config.assets.precompile += %w[sdg/**/*.png]
-Rails.application.config.assets.precompile += %w[sdg/**/*.svg]
-
-# Loads custom images and custom fonts before app/assets/images and app/assets/fonts