Upgrade Rails to version 5.2.1 and adopt code & specs where necessary

Signed-off-by: Sebastian Serth <Sebastian.Serth@student.hpi.de>

config/application.rb

@@ -1,4 +1,4 @@
-require File.expand_path('../boot', __FILE__)
+require_relative 'boot'
 
 require 'rails/all'
 
@@ -8,9 +8,13 @@ Bundler.require(*Rails.groups)
 
 module CodeOcean
   class Application < Rails::Application
+    # Initialize configuration defaults for originally generated Rails version.
+    config.load_defaults 5.0
+
     # Settings in config/environments/* take precedence over those specified here.
-    # Application configuration should go into files in config/initializers
-    # -- all .rb files in that directory are automatically loaded.
+    # Application configuration can go into files in config/initializers
+    # -- all .rb files in that directory are automatically loaded after loading
+    # the framework and any gems in your application.
 
     # Set Time.zone default to the specified zone and make Active Record auto-convert to this zone.
     # Run "rake -D time" for a list of tasks for finding time zone names. Default is UTC.
@@ -21,23 +25,8 @@ module CodeOcean
     # config.i18n.default_locale = :de
     config.i18n.available_locales = [:de, :en]
 
-    # Do not swallow errors in after_commit/after_rollback callbacks.
-    config.active_record.raise_in_transactional_callbacks = true
-
     config.autoload_paths << Rails.root.join('lib')
     config.eager_load_paths << Rails.root.join('lib')
     config.assets.precompile += %w( markdown-buttons.png )
-
-    #config.active_record.schema_format = :sql
-
-    case (RUBY_ENGINE)
-      when 'ruby'
-        # ...
-        #this is enabled in prod for testing
-        config.middleware.use ActiveRecord::ConnectionAdapters::ConnectionManagement
-      when 'jruby'
-        # plattform specific
-        java.lang.Class.for_name('javax.crypto.JceSecurity').get_declared_field('isRestricted').tap{|f| f.accessible = true; f.set nil, false}
-    end
   end
 end