Group all gems in local Gemfile

The local Gemfile (only used for CI and tooling) was grouped for
frontend and backend only yet. In order to be able to install only a
subset of gems (for generating docs for example) we should group all
gems.

Gemfile

@@ -2,36 +2,37 @@
 
 source 'https://rubygems.org'
 
-gemspec require: false
+group :backend, :frontend, :core, :api do
+  gemspec require: false
 
-rails_version = ENV['RAILS_VERSION'] || '~> 5.2.0'
-gem 'rails', rails_version, require: false
+  rails_version = ENV['RAILS_VERSION'] || '~> 5.2.0'
+  gem 'rails', rails_version, require: false
 
-platforms :ruby do
-  case ENV['DB']
-  when /mysql/
-    gem 'mysql2', '~> 0.5.0', require: false
-  when /postgres/
-    gem 'pg', '~> 1.0', require: false
-  else
-    gem 'sqlite3', require: false
-    gem 'fast_sqlite', require: false
+  platforms :ruby do
+    case ENV['DB']
+    when /mysql/
+      gem 'mysql2', '~> 0.5.0', require: false
+    when /postgres/
+      gem 'pg', '~> 1.0', require: false
+    else
+      gem 'sqlite3', require: false
+      gem 'fast_sqlite', require: false
+    end
   end
-end
 
-platforms :jruby do
-  gem 'jruby-openssl', require: false
-  gem 'activerecord-jdbcsqlite3-adapter', require: false
-end
+  platforms :jruby do
+    gem 'jruby-openssl', require: false
+    gem 'activerecord-jdbcsqlite3-adapter', require: false
+  end
 
-gem 'database_cleaner', '~> 1.3', require: false
-gem 'factory_bot_rails', '~> 4.8', require: false
-gem 'i18n-tasks', '~> 0.9', require: false
-gem 'rspec-activemodel-mocks', '~>1.1', require: false
-gem 'rspec-rails', '~> 3.7', require: false
-gem 'simplecov', require: false
-gem 'with_model', require: false
-gem 'rails-controller-testing', require: false
+  gem 'database_cleaner', '~> 1.3', require: false
+  gem 'factory_bot_rails', '~> 4.8', require: false
+  gem 'rspec-activemodel-mocks', '~>1.1', require: false
+  gem 'rspec-rails', '~> 3.7', require: false
+  gem 'simplecov', require: false
+  gem 'with_model', require: false
+  gem 'rails-controller-testing', require: false
+end
 
 group :backend, :frontend do
   gem 'capybara', '~> 2.15', require: false
@@ -49,17 +50,17 @@ group :backend do
   gem 'teaspoon-mocha', require: false
 end
 
-gem 'rubocop', '~> 0.53.0', require: false
-
 group :utils do
   gem 'pry'
   gem 'launchy', require: false
+  gem 'i18n-tasks', '~> 0.9', require: false
+  gem 'rubocop', '~> 0.53.0', require: false
 end
 
 gem 'rspec_junit_formatter', require: false, group: :ci
 
 # Documentation
-gem 'yard', require: false
+gem 'yard', require: false, group: :docs
 
 custom_gemfile = File.expand_path('Gemfile-custom', __dir__)
 eval File.read(custom_gemfile) if File.exist?(custom_gemfile)