update layout search form
remove SnippetFilesController
remove SnippetFilesView
remove SnippetFileFactory
remove SnippetFileModel
Add remove_snippet_file_table_migration
update SnippetsViewForm: remove snippet_file
update schema after migration: remove snippet file
update SnippetsController#show: remove assigns snippet_file
update SnippetsController#new: remove initial snippet_file
update SnippetModel: remove association snippet_file
update SnippetsViewShow: remove snippet file info
update routes: remove all path of snippet_file
update show_snippet_feature: remove snippet file
update SnippetModel: remove snippet file association
remove snippet file link in SnippetsViewShow
update SnippetsController#create: change return url
update SnippetModel: remove have many snippet file
update SnippetsControllerSpec: change url return