Add associations and cascade delete for foreign keys

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

app/models/packages/package.rb

 class Packages::Package < ActiveRecord::Base
   belongs_to :project
+  has_many :package_files
+  has_one :maven_metadatum
 end

db/migrate/20180720120026_create_packages_package_files.rb

@@ -3,7 +3,7 @@ class CreatePackagesPackageFiles < ActiveRecord::Migration
 
   def change
     create_table :packages_package_files do |t|
-      t.references :package, index: true, foreign_key: true, null: false
+      t.references :package, index: true, foreign_key: { on_delete: :cascade }, null: false
       t.string :file
       t.integer :file_type
       t.integer :size

db/migrate/20180720120716_create_packages_packages.rb

 class CreatePackagesPackages < ActiveRecord::Migration
   def change
     create_table :packages_packages do |t|
-      t.references :project, index: true, foreign_key: true, null: false
+      t.references :project, index: true, foreign_key: { on_delete: :cascade }, null: false
       t.string :name
       t.string :version
 

db/migrate/20180720121404_create_packages_maven_metadata.rb

 class CreatePackagesMavenMetadata < ActiveRecord::Migration
   def change
     create_table :packages_maven_metadata do |t|
-      t.references :package, index: true, foreign_key: true, null: false
+      t.references :package, index: true, foreign_key: { on_delete: :cascade }, null: false
       t.string :app_group, null: false
       t.string :app_name, null: false
       t.string :app_version, null: false