Add create_source_columns option for migrations (globalize#715)

If you use `migrate_date` option on `_create_translation_table_` method, then on roll back, `_drop_translation_table_ `fails because it try to create new columns that exist yet.

So I added create `create_source_columns` property (as reverse for `remove_source_columns`) to `_drop_translation_table_` method.

CHANGELOG.md

@@ -2,6 +2,7 @@
 
 ## Unreleased
 
+* Add `create_source_columns` option for migrations. [#715](https://github.com/globalize/globalize/pull/715) by [IlyasValiullov](https://github.com/IlyasValiullov)
 * Autosave is now configurable, but defaults to false. [#736](https://github.com/globalize/globalize/pull/736) by [James Hart](https://github.com/hjhart) 
 
 ## 5.3.0 (2019-05-14)

lib/globalize/active_record/migration.rb

@@ -62,6 +62,7 @@ def remove_source_columns
         end
 
         def drop_translation_table!(options = {})
+          add_missing_columns if options[:create_source_columns]
           move_data_to_model_table if options[:migrate_data]
           drop_translations_index
           drop_translation_table
@@ -148,8 +149,6 @@ def move_data_to_translation_table
         end
 
         def move_data_to_model_table
-          add_missing_columns
-
           # Find all of the translated attributes for all records in the model.
           all_translated_attributes = model.all.collect{|m| m.attributes}
           all_translated_attributes.each do |translated_record|

test/globalize/migration_test.rb

@@ -183,6 +183,16 @@ class MigrationTest < MiniTest::Spec
       assert !Migrated.translation_class.index_exists_on?(:locale)
     end
 
+    it 'create source columns on drops the translations table' do
+      column_before = Migrated.columns.detect { |c| c.name == 'name' }
+
+      Migrated.create_translation_table!({:name => :string}, :remove_source_columns => true)
+      Migrated.drop_translation_table!(:create_source_columns => true)
+
+      column = Migrated.columns.detect { |c| c.name == 'name' }
+      assert_equal column_before.try(:type), column.try(:type)
+    end
+
     it 'cannot be called on non-translated models' do
       assert_raises NoMethodError do
         Blog.drop_translation_table!